media: i2c: ov5645: Use v4l2_async_register_subdev_sensor()

Utilize the v4l2_async_register_subdev_sensor() helper to register the
sub-device, as this facilitates parsing of firmware interfaces for remote
references.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>