ch9200: Convert to use module_usb_driver

Converts the ch9200 driver to use the module_usb_driver() macro which
makes the code smaller and a bit simpler.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: David S. Miller <davem@davemloft.net>