Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h
index da70544..5b072ab 100644
--- a/arch/um/include/asm/mmu.h
+++ b/arch/um/include/asm/mmu.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __ARCH_UM_MMU_H