fix a braino in ovl_d_select_inode()

when opening a directory we want the overlayfs inode, not one from
the topmost layer.
Reported-By: NAndrey Jr. Melnikov <temnota.am@gmail.com>
Tested-By: NAndrey Jr. Melnikov <temnota.am@gmail.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/overlayfs/inode.c

@@ -343,6 +343,9 @@ struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
 	struct path realpath;
 	enum ovl_path_type type;
 
+	if (d_is_dir(dentry))
+		return d_backing_inode(dentry);
+
 	type = ovl_path_real(dentry, &realpath);
 	if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 		err = ovl_want_write(dentry);