media: uvcvideo: Set media controller entity functions

The media controller core prints a warning when an entity is registered
without a function being set. This affects the uvcvideo driver, as the
warning was added without first addressing the issue in existing
drivers. The problem is harmless, but unnecessarily worries users. Fix
it by mapping UVC entity types to MC entity functions as accurately as
possible using the existing functions.

Fixes: b50bde4e ("[media] v4l2-subdev: use MEDIA_ENT_T_UNKNOWN for new subdevs")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>