loader: Avoid use-after-free / use of uninitialized local variables
Per the valgrind output below, we were returning the pointer to freed memory if none of the later conditional pointer assignments were executed.
Also, we were skipping to the out: label before the vendor_id & chip_id variables used by it were initialized, resulting in broken LIBGL_DEBUG=verbose output such as
libGL: pci id for fd 4: 51108f00:51108f00, driver radeonsi
Fixes: 5a545e35 "loader: always map the "amdgpu" kernel driver name to radeonsi (v2)"
==403== Invalid read of size 1
==403== at 0x4AFD576: surfaceless_probe_device (platform_surfaceless.c:316)
==403== by 0x4AFD915: dri2_initialize_surfaceless (platform_surfaceless.c:391)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:984)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:958)
==403== by 0x4AF1EEC: _eglMatchAndInitialize (egldriver.c:75)
==403== by 0x4AF1F3B: _eglMatchDriver (egldriver.c:96)
==403== by 0x4AE9367: eglInitialize (eglapi.c:617)
==403== by 0x1D99C9: tcu::surfaceless::EglRenderContext::EglRenderContext(glu::RenderConfig const&, tcu::CommandLine const&) [clone .constprop.57] (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x1DABB0: tcu::surfaceless::ContextFactory::createContext(glu::RenderConfig const&, tcu::CommandLine const&, glu::RenderContext const*) const (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x53EBD1: glu::createRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::RenderConfig const&, glu::RenderContext const*) (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x53EFE9: glu::createDefaultRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::ApiType) (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x1DE07A: deqp::gles2::Context::Context(tcu::TestContext&) (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x1DB5EF: deqp::gles2::TestPackage::init() (in /deqp/modules/gles2/deqp-gles2)
==403== Address 0x56bd340 is 0 bytes inside a block of size 4 free'd
==403== at 0x48369AB: free (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==403== by 0x4B01767: loader_get_driver_for_fd (loader.c:464)
==403== by 0x4AFD553: surfaceless_probe_device (platform_surfaceless.c:308)
==403== by 0x4AFD915: dri2_initialize_surfaceless (platform_surfaceless.c:391)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:984)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:958)
==403== by 0x4AF1EEC: _eglMatchAndInitialize (egldriver.c:75)
==403== by 0x4AF1F3B: _eglMatchDriver (egldriver.c:96)
==403== by 0x4AE9367: eglInitialize (eglapi.c:617)
==403== by 0x1D99C9: tcu::surfaceless::EglRenderContext::EglRenderContext(glu::RenderConfig const&, tcu::CommandLine const&) [clone .constprop.57] (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x1DABB0: tcu::surfaceless::ContextFactory::createContext(glu::RenderConfig const&, tcu::CommandLine const&, glu::RenderContext const*) const (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x53EBD1: glu::createRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::RenderConfig const&, glu::RenderContext const*) (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x53EFE9: glu::createDefaultRenderContext(tcu::Platform&, tcu::CommandLine const&, glu::ApiType) (in /deqp/modules/gles2/deqp-gles2)
==403== Block was alloc'd at
==403== at 0x483577F: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==403== by 0x4EE5E09: strndup (strndup.c:43)
==403== by 0x4B010B1: loader_get_kernel_driver_name (loader.c:101)
==403== by 0x4B016AF: loader_get_driver_for_fd (loader.c:462)
==403== by 0x4AFD553: surfaceless_probe_device (platform_surfaceless.c:308)
==403== by 0x4AFD915: dri2_initialize_surfaceless (platform_surfaceless.c:391)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:984)
==403== by 0x4AF5EEA: dri2_initialize (egl_dri2.c:958)
==403== by 0x4AF1EEC: _eglMatchAndInitialize (egldriver.c:75)
==403== by 0x4AF1F3B: _eglMatchDriver (egldriver.c:96)
==403== by 0x4AE9367: eglInitialize (eglapi.c:617)
==403== by 0x1D99C9: tcu::surfaceless::EglRenderContext::EglRenderContext(glu::RenderConfig const&, tcu::CommandLine const&) [clone .constprop.57] (in /deqp/modules/gles2/deqp-gles2)
==403== by 0x1DABB0: tcu::surfaceless::ContextFactory::createContext(glu::RenderConfig const&, tcu::CommandLine const&, glu::RenderContext const*) const (in /deqp/modules/gles2/deqp-gles2)