rt2x00: Identify rt2800usb chipsets.

commit bc93eda7e903ff75cefcb6e247ed9b8e9f8e9783 upstream.

According to the latest USB ID database these are all RT2770 / RT2870 / RT307x
devices.

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>
[bwh: Backported to 3.2: adjust context for previously cherry-picked
 commit d42a179b941a9e4cc6cf41d0f3cbadd75fc48a89 'rt2x00: Add support
 for D-Link DWA-127 to rt2800usb']
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>