Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/mips/alchemy/common/vss.c b/arch/mips/alchemy/common/vss.c
index a7bd32e..3d0d468 100644
--- a/arch/mips/alchemy/common/vss.c
+++ b/arch/mips/alchemy/common/vss.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Au1300 media block power gating (VSS)
  *