rsi: Use module_usb_driver

module_usb_driver eliminates the boilerplate and makes the code simpler,
in addition to the fact currently rsi_module_init() ignores usb_deregister() error.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>