ath5k: remove _bh from inner locks

spin_unlock_bh(&txq->lock) already disables softirqs so we don't want
to do it here.  Fixes smatch warnings:

   drivers/net/wireless/ath/ath5k/base.c:1048 ath5k_drain_tx_buffs() error: double lock 'bottom_half:'
   drivers/net/wireless/ath/ath5k/base.c:1056 ath5k_drain_tx_buffs() error: double unlock 'bottom_half:'
Reported-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/base.c

@@ -1045,11 +1045,11 @@ ath5k_drain_tx_buffs(struct ath5k_hw *ah)
 
 				ath5k_txbuf_free_skb(ah, bf);
 
-				spin_lock_bh(&ah->txbuflock);
+				spin_lock(&ah->txbuflock);
 				list_move_tail(&bf->list, &ah->txbuf);
 				ah->txbuf_len++;
 				txq->txq_len--;
-				spin_unlock_bh(&ah->txbuflock);
+				spin_unlock(&ah->txbuflock);
 			}
 			txq->link = NULL;
 			txq->txq_poll_mark = false;