ath9k: Fix a locking related issue.

Spin_lock has been tried to be acquired twice from ath9k_tasklet
to ath_reset which resulted in a machine freeze.
Signed-off-by: Vivek Natarajan <vnatarajan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -563,8 +563,11 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
 
 	rcu_read_unlock();
 
-	if (needreset)
+	if (needreset) {
+		spin_unlock_bh(&sc->sc_pcu_lock);
 		ath_reset(sc, false);
+		spin_lock_bh(&sc->sc_pcu_lock);
+	}
 }
 
 static u32 ath_lookup_rate(struct ath_softc *sc, struct ath_buf *bf,