Free io_u related structures before killing IO engine

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/backend.c b/backend.c
index 1b5c2eb..a71d768 100644
--- a/backend.c
+++ b/backend.c
@@ -1287,8 +1287,8 @@
 		verify_async_exit(td);
 
 	close_and_free_files(td);
-	close_ioengine(td);
 	cleanup_io_u(td);
+	close_ioengine(td);
 	cgroup_shutdown(td, &cgroup_mnt);
 
 	if (td->o.cpumask_set) {