Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/perf/util/jitdump.h b/tools/perf/util/jitdump.h
index c6b9b67..f2c3823 100644
--- a/tools/perf/util/jitdump.h
+++ b/tools/perf/util/jitdump.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * jitdump.h: jitted code info encapsulation file format
  *