Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/um/drivers/port.h b/arch/um/drivers/port.h
index 372a80c..9085b33 100644
--- a/arch/um/drivers/port.h
+++ b/arch/um/drivers/port.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __PORT_H__