Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/Documentation/media/frontend.h.rst.exceptions b/Documentation/media/frontend.h.rst.exceptions
index f7c4df6..6283702 100644
--- a/Documentation/media/frontend.h.rst.exceptions
+++ b/Documentation/media/frontend.h.rst.exceptions
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
 # Ignore header name
 ignore define _DVBFRONTEND_H_