config: Fix platform busid parsing when there is no ID_PATH prop

On at least Lenovo Thinkpad E585 udev does not have ID_PATH property for
the drm node (see
xorg/xserver#993). While this is
likely udev bug, this causes the device to be not recognized as
attribs->busid is NULL, which causes platform_find_pci_info to be not
called and corresponding xf86_platform_devices[i]->pdev to be NULL.

At this moment pdev being NULL will cause a crash, but this is a
different bug.

Fixes: xorg/xserver#993
Fixes:  0816e8fc linux: Make platform device probe less fragile
Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
4 jobs for fix-platform-busid-udev-no-id-path in 4 minutes and 2 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #8627145
debian-buster

00:00:13

 
  Build And Test
passed #8627146
autotools

00:03:48

passed #8627147
meson

00:01:24

passed #8627148
meson-noglamor

00:01:20