ath9k: add missing locking around ath9k_hw_proc_mib_event

ath9k_hw_proc_mib_event updates the cycle counters, so it common->cc_lock
must be acquired.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/main.c b/drivers/net/wireless/ath/ath9k/main.c
index 74ff51d..2c7f28e 100644
--- a/drivers/net/wireless/ath/ath9k/main.c
+++ b/drivers/net/wireless/ath/ath9k/main.c
@@ -779,7 +779,9 @@
 		 * it will clear whatever condition caused
 		 * the interrupt.
 		 */
+		spin_lock(&common->cc_lock);
 		ath9k_hw_proc_mib_event(ah);
+		spin_unlock(&common->cc_lock);
 		ath9k_hw_set_interrupts(ah, ah->imask);
 	}