Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/atm/atmtcp.c b/drivers/atm/atmtcp.c
index afebeb1..d9fd702 100644
--- a/drivers/atm/atmtcp.c
+++ b/drivers/atm/atmtcp.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /* drivers/atm/atmtcp.c - ATM over TCP "device" driver */
 
 /* Written 1997-2000 by Werner Almesberger, EPFL LRC/ICA */