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")
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240110090111.458115-1-alexander.stein@ew.tq-group.com