Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index be02507..ca639ed 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/export.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/task.h>