lws actually *requires* trees when built with hwloc

src/sched_policies/work_stealing_policy.c

@@ -533,5 +533,9 @@ struct starpu_sched_policy _starpu_sched_lws_policy =
 	.pop_every_task = NULL,
 	.policy_name = "lws",
 	.policy_description = "locality work stealing",
+#ifdef STARPU_HAVE_HWLOC
+	.worker_type = STARPU_WORKER_TREE,
+#else
 	.worker_type = STARPU_WORKER_LIST,
+#endif
 };