Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/net/ethernet/rdc/Makefile b/drivers/net/ethernet/rdc/Makefile
index 8d51fd2..8074654 100644
--- a/drivers/net/ethernet/rdc/Makefile
+++ b/drivers/net/ethernet/rdc/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 #
 # Makefile for the RDC network device drivers.
 #