cfg80211: fix P2P-Device stop locking

cfg80211_stop_p2p_device() requires the devlist_mtx to
be held, but nl80211_stop_p2p_device() doesn't acquire
it which is a locking error and causes a warning (when
lockdep is enabled). Fix this.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -8159,9 +8159,11 @@ static int nl80211_stop_p2p_device(struct sk_buff *skb, struct genl_info *info)
 	if (!rdev->ops->stop_p2p_device)
 		return -EOPNOTSUPP;
 
+	mutex_lock(&rdev->devlist_mtx);
 	mutex_lock(&rdev->sched_scan_mtx);
 	cfg80211_stop_p2p_device(rdev, wdev);
 	mutex_unlock(&rdev->sched_scan_mtx);
+	mutex_unlock(&rdev->devlist_mtx);
 
 	return 0;
 }