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

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
4 jobs for fix-pci-device-null-reference in 5 minutes and 3 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #8630738
debian-buster

00:00:14

 
  Build And Test
passed #8630739
autotools

00:04:48

passed #8630740
meson

00:02:10

passed #8630741
meson-noglamor

00:01:53