rt2800usb: fix RX descriptor naming

Rename RXD_W0_* defines to RXINFO_W0_* ones to match naming
used for TX descriptor and by the vendor driver.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>