Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index c90817b..0021d7f 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <linux/posix_types.h>