ath9k: Use atomic operations

The 'sc_flags' variable is being used in a number of places
with no locking whatsoever. This patch converts the usage
of sc_flags to atomic ops.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 6619a39..bb74780 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -1536,7 +1536,7 @@
 	int i;
 	u32 npend = 0;
 
-	if (sc->sc_flags & SC_OP_INVALID)
+	if (test_bit(SC_OP_INVALID, &sc->sc_flags))
 		return true;
 
 	ath9k_hw_abort_tx_dma(ah);