media: uvcvideo: Move video_device under video_queue

It is more natural that the "struct video_device" belongs to
uvc_video_queue instead of uvc_streaming.

This is an aesthetic change. No functional change expected.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans de Goede <hansg@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>