xfree86: Fix potentially NULL reference to platform device's PCI device

xf86_platform_devices[i].pdev may be NULL in cases we fail to parse the
busid in config_udev_odev_setup_attribs() (see also [1], [2]) such as
when udev does not give use ID_PATH. This in turn leads to
platform_find_pci_info() being not called and pdev being NULL.

[1]: xorg/xserver#993
[2]: xorg/xserver#1076

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
5 jobs for master in 7 minutes and 40 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-buster #11236671

00:00:22

 
  Build And Test
passed autotools #11236672

00:07:17

passed meson #11236673

00:05:08

passed meson-noglamor #11236674

00:03:48

passed mingw-cross-build #11236675

00:01:20