Fix spurious assertion

src/datawizard/coherency.c

@@ -745,7 +745,7 @@ int _starpu_fetch_data_on_node(starpu_data_handle_t handle, int node, struct _st
 	if (cpt == STARPU_SPIN_MAXTRY)
 		_starpu_spin_lock(&handle->header_lock);
 
-	if (is_prefetch > STARPU_FETCH)
+	if (mode & STARPU_R && is_prefetch > STARPU_FETCH)
 	{
 		unsigned src_node_mask = 0;