Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/kernel/debug/kdb/kdb_keyboard.c b/kernel/debug/kdb/kdb_keyboard.c
index 118527a..750497b 100644
--- a/kernel/debug/kdb/kdb_keyboard.c
+++ b/kernel/debug/kdb/kdb_keyboard.c
@@ -173,11 +173,11 @@
 	case KT_LATIN:
 		if (isprint(keychar))
 			break;		/* printable characters */
-		/* drop through */
+		/* fall through */
 	case KT_SPEC:
 		if (keychar == K_ENTER)
 			break;
-		/* drop through */
+		/* fall through */
 	default:
 		return -1;	/* ignore unprintables */
 	}