wl12xx: protect wl12xx_op_set_rts_threshold()

The function doesn't lock the mutex before sending the acx.
Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Reviewed-by: Vidhya Govindan <vidhya.govindan@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/main.c

@@ -957,11 +957,15 @@ static int wl12xx_op_set_rts_threshold(struct ieee80211_hw *hw, u32 value)
 	struct wl12xx *wl = hw->priv;
 	int ret;
 
+	mutex_lock(&wl->mutex);
+
 	ret = wl12xx_acx_rts_threshold(wl, (u16) value);
 
 	if (ret < 0)
 		wl12xx_warning("wl12xx_op_set_rts_threshold failed: %d", ret);
 
+	mutex_unlock(&wl->mutex);
+
 	return ret;
 }