Avoid using the rbtree if we don't have to

Basically reinstate the old logic of not sorting when it's
not a win for reading the data back.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index 6a3a87b..bed1e28 100644
--- a/fio.c
+++ b/fio.c
@@ -736,6 +736,7 @@
 	INIT_LIST_HEAD(&td->io_u_busylist);
 	INIT_LIST_HEAD(&td->io_u_requeues);
 	INIT_LIST_HEAD(&td->io_log_list);
+	INIT_LIST_HEAD(&td->io_hist_list);
 	td->io_hist_tree = RB_ROOT;
 
 	if (init_io_u(td))