Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/target/loopback/Makefile b/drivers/target/loopback/Makefile
index 6abebdf..336bd44 100644
--- a/drivers/target/loopback/Makefile
+++ b/drivers/target/loopback/Makefile
@@ -1 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_LOOPBACK_TARGET)	+= tcm_loop.o