Fix non-fxt build

src/drivers/mic/driver_mic_source.c

@@ -523,8 +523,10 @@ void *_starpu_mic_src_worker(void *arg)
 	/* unsigned memnode = baseworker->memory_node; */
 
 	_starpu_driver_start(baseworker, _STARPU_FUT_MIC_KEY, 0);
+#ifdef STARPU_USE_FXT
 	for (i = 1; i < worker_set->nworkers; i++)
 		_starpu_worker_start(&worker_set->workers[i], _STARPU_FUT_MIC_KEY, 0);
+#endif
 
 	// Current task for a thread managing a worker set has no sense.
 	_starpu_set_current_task(NULL);