mac80211: unlock on error path in ieee80211_ibss_join()

We recently introduced a new return here but it needs an unlock first.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ibss.c

@@ -993,9 +993,11 @@ int ieee80211_ibss_join(struct ieee80211_sub_if_data *sdata,
 	if (params->channel_fixed) {
 		sdata->local->oper_channel = params->channel;
 		if (!ieee80211_set_channel_type(sdata->local, sdata,
-					       params->channel_type))
+					       params->channel_type)) {
+			mutex_unlock(&sdata->u.ibss.mtx);
 			return -EINVAL;
 		}
+	}
 
 	if (params->ie) {
 		sdata->u.ibss.ie = kmemdup(params->ie, params->ie_len,