rt2x00: Input-polldev requires input device

input-polldev requires a correctly allocated
and initialized input device to be set for the
input_polled_dev->input field.
Failure to do that will prevent correct polling
of the device.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>