mac80211: fix debugfs netdev rename

If, for some reason, a netdev has no debugfs dir, we shouldn't
try to rename that dir.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/debugfs_netdev.c

@@ -545,8 +545,12 @@ static int netdev_notify(struct notifier_block *nb,
 
 	sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 
-	sprintf(buf, "netdev:%s", dev->name);
 	dir = sdata->debugfsdir;
+
+	if (!dir)
+		return 0;
+
+	sprintf(buf, "netdev:%s", dev->name);
 	if (!debugfs_rename(dir->d_parent, dir, dir->d_parent, buf))
 		printk(KERN_ERR "mac80211: debugfs: failed to rename debugfs "
 		       "dir to %s\n", buf);