cfg80211: fix debugfs error handling

If something goes wrong creating the debugfs dir or when
debugfs is not compiled in, the current code might lead to
trouble; make it more robust.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/core.c

@@ -184,7 +184,8 @@ int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
 	if (result)
 		goto out_unlock;
 
-	if (!debugfs_rename(rdev->wiphy.debugfsdir->d_parent,
+	if (rdev->wiphy.debugfsdir &&
+	    !debugfs_rename(rdev->wiphy.debugfsdir->d_parent,
 			    rdev->wiphy.debugfsdir,
 			    rdev->wiphy.debugfsdir->d_parent,
 			    newname))
@@ -317,6 +318,8 @@ int wiphy_register(struct wiphy *wiphy)
 	drv->wiphy.debugfsdir =
 		debugfs_create_dir(wiphy_name(&drv->wiphy),
 				   ieee80211_debugfs_dir);
+	if (IS_ERR(drv->wiphy.debugfsdir))
+		drv->wiphy.debugfsdir = NULL;
 
 	res = 0;
 out_unlock: