rt2x00: Add rt2870 device id for Dvico usb key

This patch add a device id for the wifi usb keys shiped by DVICO with
some of their tvix hardware.

Signed-off-by: Anthony Bourguignon <contact+kernel@toniob.net>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>