media: uvcvideo: Return the number of processed controls

commit ba4fafb02ad6a4eb2e00f861893b5db42ba54369 upstream.

If we let know our callers that we have not done anything, they will be
able to optimize their decisions.

Cc: stable@kernel.org
Fixes: b4012002 ("[media] uvcvideo: Add support for control events")
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Message-ID: <20250224-uvc-data-backup-v2-1-de993ed9823b@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>