Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/alpha/math-emu/math.c b/arch/alpha/math-emu/math.c
index 1c2d456..d568cd9 100644
--- a/arch/alpha/math-emu/math.c
+++ b/arch/alpha/math-emu/math.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/kernel.h>