Use the new v4l2_subdev_internal_ops release op to free the
subdev memory only when the last user closed the file handle.

Move v4l2_device_unregister_subdev() to the end of the
vimc_ent_sd_unregister() function since now the unregister_subdev()
call may free the vimc_ent_device struct which is used after the
unregister_subdev() call. So this now has to be done last.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>