media: v4l: async: Set owner for async sub-devices

Set the owner field of the async sub-devices by making
v4l2_async_register_subdev() a macro and obtaining THIS_MODULE that way.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>