ath9k: Use mutex_lock to avoid potential race in start/stop rng

Move ath9k_rng_stop/ath9k_rng_start pair into critical section,
use mutex_lock to void potential race accessing.
Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

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

@@ -731,12 +731,12 @@ static int ath9k_start(struct ieee80211_hw *hw)
 
 	spin_unlock_bh(&sc->sc_pcu_lock);
 
+	ath9k_rng_start(sc);
+
 	mutex_unlock(&sc->mutex);
 
 	ath9k_ps_restore(sc);
 
-	ath9k_rng_start(sc);
-
 	return 0;
 }
 
@@ -826,10 +826,10 @@ static void ath9k_stop(struct ieee80211_hw *hw)
 
 	ath9k_deinit_channel_context(sc);
 
-	ath9k_rng_stop(sc);
-
 	mutex_lock(&sc->mutex);
 
+	ath9k_rng_stop(sc);
+
 	ath_cancel_work(sc);
 
 	if (test_bit(ATH_OP_INVALID, &common->op_flags)) {