usb: fix build warning in pci-quirks.h when CONFIG_PCI is not enabled

Fix warning when CONFIG_PCI is not enabled
(from commit 29636578).

drivers/usb/host/pci-quirks.h: 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@infradead.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Moiz Sonasath <m-sonasath@ti.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>