When the TX status handler failed to clear the queue
in rt2x00usb_watchdog_tx_dma() we shouldn't use a failsave
to use the rt2x00usb txdone handler.

If a driver has overriden the txdone handler it must make
sure the txdone handler is capable of cleaning up the queue itself.
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Acked-by: NGertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>