Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/mips/include/asm/serial.h b/arch/mips/include/asm/serial.h
index 1d830c6..2777148 100644
--- a/arch/mips/include/asm/serial.h
+++ b/arch/mips/include/asm/serial.h
@@ -1,10 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  * Copyright (C) 2017 MIPS Tech, LLC
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License as published by the
- * Free Software Foundation;  either version 2 of the  License, or (at your
- * option) any later version.
  */
 #ifndef __ASM__SERIAL_H
 #define __ASM__SERIAL_H