rt2x00usb: check USB's request error code in rt2800usb_autorun_detect()

rt2800usb_autorun_detect() blindly assumes assumes that it worked while
it could have failed. Check the error code here.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>