Wireless: nl80211, fix lock imbalance

Don't forget to unlock cfg80211_mutex in one fail path of
nl80211_set_wiphy.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/nl80211.c

@@ -447,6 +447,7 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 
 	rdev = __cfg80211_drv_from_info(info);
 	if (IS_ERR(rdev)) {
+		mutex_unlock(&cfg80211_mutex);
 		result = PTR_ERR(rdev);
 		goto unlock;
 	}