Fix missing ';' before slave disk utilization in terse output

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/diskutil.c b/diskutil.c
index 4ddaa33..c1524a0 100644
--- a/diskutil.c
+++ b/diskutil.c
@@ -470,7 +470,7 @@
 				agg->time_in_queue / agg->slavecount,
 				agg->max_util.u.f);
 	} else {
-		log_info("slaves;%u;%u;%u;%u;%u;%u;%u;%3.2f%%",
+		log_info(";slaves;%u;%u;%u;%u;%u;%u;%u;%3.2f%%",
 				agg->ios[0] / agg->slavecount,
 				agg->ios[1] / agg->slavecount,
 				agg->merges[0] / agg->slavecount,