Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/kernel/power/poweroff.c b/kernel/power/poweroff.c
index 7ef6866..6d47528 100644
--- a/kernel/power/poweroff.c
+++ b/kernel/power/poweroff.c
@@ -1,7 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * poweroff.c - sysrq handler to gracefully power down machine.
- *
- * This file is released under the GPL v2
  */
 
 #include <linux/kernel.h>