rt2x00: Add device ID for Epson WN7512BEP

Make Epson WN7512BEP work by adding its device-id to rt2800usb. Device
contains a Ralink RT3071L, registers as vendor Accton/Arcadyan.

Signed-off-by: Tom Gaudasinski <tomg@records.headdesk.com.au>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>