clover: Add constructor for sampler_argument.

Fix defects reported by Coverity Scan.

member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize s.
member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize st.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
36 jobs for !8657 with fix-cid-1213937 in 10 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #7710530
sanity

00:00:10

 
  Container
manual #7710535
aarch64 manual
arm_build
manual #7710537
manual
arm_test-base
manual #7710538
windows shell 1809 mesa manual
windows_build_vs2019
manual #7710531
manual
x86_build-base
manual #7710533
manual
x86_test-base
 
  Container 2
created #7710553
android_build
created #7710558
arm64_test
created #7710560
armhf_test
created #7710548
i386_build
created #7710540
kernel+rootfs_amd64
created #7710542
aarch64
kernel+rootfs_arm64
created #7710544
aarch64
kernel+rootfs_armhf
created #7710550
ppc64el_build
created #7710552
s390x_build
created #7710546
x86_build
created #7710555
x86_test-gl
created #7710557
x86_test-vk
 
  Meson X86 64
created #7710570
meson-clang
created #7710572
meson-clover
created #7710565
meson-clover-testing
created #7710567
gstreamer
meson-gallium
created #7710569
meson-release
created #7710562
meson-testing
created #7710564
meson-testing-asan
created #7710574
meson-vulkan
 
  Build Misc
created #7710576
meson-android
created #7710579
aarch64
meson-arm64
created #7710581
aarch64
meson-arm64-asan
created #7710583
aarch64
meson-arm64-build-test
created #7710577
aarch64
meson-armhf
created #7710585
meson-i386
created #7710591
meson-mingw32-x86_64
created #7710589
kvm
meson-ppc64el
created #7710587
kvm
meson-s390x
 
  Software Renderer
created #7710593
llvmpipe-piglit-cl