ext3 uses rb_node = NULL; to zero rb_root.

The problem with this is that 17d9ddc72fb8bba0d4f678 ("rbtree: Add support
for augmented rbtrees") in the linux-next tree adds a new field to that
struct which needs to be NULLas well.  This patch uses RB_ROOT as the
intializer so all of the relevant fields will be NULL'd.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Eric Paris <eparis@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext3/dir.c

@@ -297,7 +297,7 @@ static void free_rb_tree_fname(struct rb_root *root)
 			kfree (old);
 		}
 		if (!parent)
-			root->rb_node = NULL;
+			*root = RB_ROOT;
 		else if (parent->rb_left == n)
 			parent->rb_left = NULL;
 		else if (parent->rb_right == n)