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
Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
5 jobs for fix-platform-busid-udev-no-id-path in 6 minutes and 6 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Docker Image
passed debian-buster #11285554

00:00:19

 
  Build And Test
passed autotools #11285555

00:05:46

passed meson #11285556

00:01:29

passed meson-noglamor #11285557

00:01:38

passed mingw-cross-build #11285558

00:00:51