vga_switcheroo.h: fix pci_dev warning

Fix warnings on some architectures/configs (not on x86):

include/linux/vga_switcheroo.h:28:30: warning: 'struct pci_dev' declared inside parameter list [enabled by default]
include/linux/vga_switcheroo.h:28:30: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc:	Takashi Iwai <tiwai@suse.de>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>