Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/sparc/kernel/helpers.S b/arch/sparc/kernel/helpers.S
index e4e5b83..9b3f747 100644
--- a/arch/sparc/kernel/helpers.S
+++ b/arch/sparc/kernel/helpers.S
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 	.align	32
 	.globl	__flushw_user
 	.type	__flushw_user,#function