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 586bc4aa ("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.

Fixes: 586bc4aa ("ALSA: hda/hdmi - fix vgaswitcheroo detection for AMD")
Link: https://lore.kernel.org/r/PSXP216MB0438BFEAA0617283A834E11580580@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM/Reported-and-tested-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Alexander Deucher <alexander.deucher@amd.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Link: https://lore.kernel.org/r/77aa6c01aefe1ebc4004e87b0bc714f2759f15c4.1575985006.git.lukas@wunner.deSigned-off-by: Takashi Iwai <tiwai@suse.de>