media: tc358743: register v4l2 async device only after successful setup

Ensure the device has been setup correctly before registering the v4l2
async device, thus allowing userspace to access.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Fixes: 4c5211a1 ("[media] tc358743: register v4l2 asynchronous subdevice")
Cc: stable@vger.kernel.org
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>