rt2x00: Add USB device ID of Buffalo WLI-UC-GNHP.

This is reported to be an RT3070 based device.

Reported-by: Teika Kazura <teika@lavabit.com>
Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>