Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/Documentation/media/kapi/v4l2-clocks.rst b/Documentation/media/kapi/v4l2-clocks.rst
index b8a8958..5c22eec 100644
--- a/Documentation/media/kapi/v4l2-clocks.rst
+++ b/Documentation/media/kapi/v4l2-clocks.rst
@@ -1,3 +1,5 @@
+.. SPDX-License-Identifier: GPL-2.0
+
 V4L2 clocks
 -----------