Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/lib/pm-notifier-error-inject.c b/lib/pm-notifier-error-inject.c
index c094b2d..5d89f0d 100644
--- a/lib/pm-notifier-error-inject.c
+++ b/lib/pm-notifier-error-inject.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/suspend.h>