Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/gpio/gpio-hammer.c b/tools/gpio/gpio-hammer.c
index 4bcb234..0e0060a 100644
--- a/tools/gpio/gpio-hammer.c
+++ b/tools/gpio/gpio-hammer.c
@@ -1,12 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * gpio-hammer - example swiss army knife to shake GPIO lines on a system
  *
  * Copyright (C) 2016 Linus Walleij
  *
- * 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.
- *
  * Usage:
  *	gpio-hammer -n <device-name> -o <offset1> -o <offset2>
  */