Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/net/atm/mpc.c b/net/atm/mpc.c
index 24b53c4..033871e 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
 
 #include <linux/kernel.h>