Free disk util on exit, not on stats display

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/backend.c b/backend.c
index ec42a5c..4c271ba 100644
--- a/backend.c
+++ b/backend.c
@@ -1663,6 +1663,7 @@
 	for_each_td(td, i)
 		fio_options_free(td);
 
+	free_disk_util();
 	cgroup_kill(cgroup_list);
 	sfree(cgroup_list);
 	sfree(cgroup_mnt);