Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/testing/selftests/timers/adjtick.c b/tools/testing/selftests/timers/adjtick.c
index 0caca3a..54d8d87 100644
--- a/tools/testing/selftests/timers/adjtick.c
+++ b/tools/testing/selftests/timers/adjtick.c
@@ -136,6 +136,7 @@
 
 	eppm = get_ppm_drift();
 	printf("%lld usec, %lld ppm", systick + (systick * eppm / MILLION), eppm);
+	fflush(stdout);
 
 	tx1.modes = 0;
 	adjtimex(&tx1);