rt2x00: Initialize QID from queue->qid

The QID_MGMT is assigned to the beacon and atim queue
during initialization. This means we don't need a seperate
check in write_tx_desc()..

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>