aufs: for v5.3-rc3, update UAPI SPDX

Simply follows the commit in mainline,
	622445541b75 2019-07-29 kbuild: detect missing "WITH
		Linux-syscall-note" for uapi headers
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

include/uapi/linux/aufs_type.h

-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 /*
  * Copyright (C) 2005-2019 Junjiro R. Okajima
  */