rt2x00: rt2800usb: nuke rt2800usb_ops_5592

It is exactly the same like the generic rt2800usb_ops.
Remove the duplicate and use the generic ops for all
devices.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>