Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/kernel/sched/wait_bit.c b/kernel/sched/wait_bit.c
index c67c6d2..45eba18 100644
--- a/kernel/sched/wait_bit.c
+++ b/kernel/sched/wait_bit.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * The implementation of the wait_bit*() and related waiting APIs:
  */