V4L/DVB (11440): PWC: fix build error when CONFIG_INPUT=m

Fix build errors when USB_PWC=y and INPUT=m.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>