Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/siox/Kconfig b/drivers/siox/Kconfig
index 083d2e6..4326db3 100644
--- a/drivers/siox/Kconfig
+++ b/drivers/siox/Kconfig
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 menuconfig SIOX
 	tristate "Eckelmann SIOX Support"
 	help
diff --git a/drivers/siox/Makefile b/drivers/siox/Makefile
index a956f65..8b5ebb1 100644
--- a/drivers/siox/Makefile
+++ b/drivers/siox/Makefile
@@ -1,2 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_SIOX) += siox-core.o
 obj-$(CONFIG_SIOX_BUS_GPIO) += siox-bus-gpio.o