Nicholas Johnson reports a null pointer deref as well as a refcount
underflow upon hot-removal of a Thunderbolt-attached AMD eGPU.
He's bisected the issue down to commit 586bc4aab878 ("ALSA: hda/hdmi -
fix vgaswitcheroo detection for AMD").
The commit iterates over PCI devices using pci_get_class() and
unreferences each device found, even though pci_get_class()
subsequently unreferences the device as well. Fix it.