Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/char/nwbutton.c b/drivers/char/nwbutton.c
index a7113b7..ea378c0 100644
--- a/drivers/char/nwbutton.c
+++ b/drivers/char/nwbutton.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * 	NetWinder Button Driver-
  *	Copyright (C) Alex Holden <alex@linuxhacker.org> 1998, 1999.