Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/mm/zbud.c b/mm/zbud.c
index 28458f7..de5dd4d 100644
--- a/mm/zbud.c
+++ b/mm/zbud.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * zbud.c
  *