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/pci.c b/drivers/net/wireless/ath/ath9k/pci.c
index 6ec9f88..aa0e83a 100644
--- a/drivers/net/wireless/ath/ath9k/pci.c
+++ b/drivers/net/wireless/ath/ath9k/pci.c
@@ -251,7 +251,7 @@
 	sc->mem = mem;
 
 	/* Will be cleared in ath9k_start() */
-	sc->sc_flags |= SC_OP_INVALID;
+	set_bit(SC_OP_INVALID, &sc->sc_flags);
 
 	ret = request_irq(pdev->irq, ath_isr, IRQF_SHARED, "ath9k", sc);
 	if (ret) {