vfs: for usbfs, etc. internal vfsmounts ->mnt_sb->s_root == ->mnt_root

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/configfs/dir.c

@@ -312,7 +312,7 @@ static int configfs_create_dir(struct config_item * item, struct dentry *dentry)
 	if (item->ci_parent)
 		parent = item->ci_parent->ci_dentry;
 	else if (configfs_mount && configfs_mount->mnt_sb)
-		parent = configfs_mount->mnt_sb->s_root;
+		parent = configfs_mount->mnt_root;
 	else
 		return -EFAULT;