Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/sound/isa/adlib.c b/sound/isa/adlib.c
index 5fb619e..5105524 100644
--- a/sound/isa/adlib.c
+++ b/sound/isa/adlib.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * AdLib FM card driver.
  */