ath5k: remove some unneeded error handling code

th5k_hw_setup_tx_queue() returns a valid offset into the ah->ah_txq[]
array.  The ah->ah_txq[] and the ah->txqs[] array are the same size.
Both have AR5K_NUM_TX_QUEUES elements.  So this error handling code
will never trigger.

Also it's wrong.  The call to ath5k_hw_release_tx_queue() with a qnum
of AR5K_NUM_TX_QUEUES or more will just trigger a WARN_ON() and
return.  Or if it missed the WARN_ON(), it would just corrupt some
memory and return.

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