Fix segfault race on exit for platforms that don't have disk util support

We still need to quisce the disk util thread, as it also functions
as the runtime ETA status printer.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/diskutil.c b/diskutil.c
index d2c0b97..d98e39a 100644
--- a/diskutil.c
+++ b/diskutil.c
@@ -15,7 +15,6 @@
 static struct disk_util *last_du;
 
 static struct fio_mutex *disk_util_mutex;
-static int disk_util_exit;
 
 FLIST_HEAD(disk_list);
 
@@ -539,16 +538,13 @@
 		agg->max_util.u.f = 100.0;
 }
 
-void free_disk_util(void)
+void disk_util_prune_entries(void)
 {
-	struct disk_util *du;
-
-	disk_util_exit = 1;
-	wait_for_disk_thread_exit();
-
 	fio_mutex_down(disk_util_mutex);
 
 	while (!flist_empty(&disk_list)) {
+		struct disk_util *du;
+
 		du = flist_entry(disk_list.next, struct disk_util, list);
 		flist_del(&du->list);
 		disk_util_free(du);