Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/mips/ralink/prom.c b/arch/mips/ralink/prom.c
index 23198c9..02e7878 100644
--- a/arch/mips/ralink/prom.c
+++ b/arch/mips/ralink/prom.c
@@ -1,7 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
- *  This program is free software; you can redistribute it and/or modify it
- *  under the terms of the GNU General Public License version 2 as published
- *  by the Free Software Foundation.
  *
  *  Copyright (C) 2009 Gabor Juhos <juhosg@openwrt.org>
  *  Copyright (C) 2010 Joonas Lahtinen <joonas.lahtinen@gmail.com>