ath9k: remove some bogus error handling code

If "axq_qnum >= ARRAY_SIZE(sc->tx.txq)", then the call to
ath9k_hw_releasetxqueue() would read beyond the end of the ah->txq[]
array and possibly corrupt memory.  Fortunately,
ath9k_hw_setuptxqueue() doesn't return high values of "axq_qnum" and
this code can be removed.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>