Fix problem with bw log not working for writes

We inadvertently only updated the read stat sample time cache,
so writes never logged any activity since negativ time spent is
rounded to zero.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index ba9e384..7ad1b57 100644
--- a/fio.c
+++ b/fio.c
@@ -1105,7 +1105,10 @@
 	clear_state = 0;
 	while (keep_running(td)) {
 		fio_gettime(&td->start, NULL);
-		memcpy(&td->ts.stat_sample_time, &td->start, sizeof(td->start));
+		memcpy(&td->ts.stat_sample_time[0], &td->start,
+				sizeof(td->start));
+		memcpy(&td->ts.stat_sample_time[1], &td->start,
+				sizeof(td->start));
 		memcpy(&td->tv_cache, &td->start, sizeof(td->start));
 
 		if (td->o.ratemin[0] || td->o.ratemin[1])