Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/misc/echo/Makefile b/drivers/misc/echo/Makefile
index 7d4caac..5b97467 100644
--- a/drivers/misc/echo/Makefile
+++ b/drivers/misc/echo/Makefile
@@ -1 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_ECHO) += echo.o