[media] usbtv: fix compiler error due to missing module.h

usbtv-video.c needs module.h. So move the module.h include from usbtv-core.c to usbtv.h,
that way both core.c and video.c have it.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>