mpi: Fix allocating req->ptr

    The unpack method will use starpu_free_on_node, and
    _starpu_mpi_handle_request_termination uses it as well, so allocation
    should also use that.

mpi/src/nmad/starpu_mpi_nmad_unknown_datatype.c

@@ -130,7 +130,7 @@ static void _starpu_mpi_unknown_datatype_recv_callback(nm_sr_event_t event, cons
 		int ret = nm_sr_recv_peek(req->backend->session, &(req->backend->data_request), &(req->backend->unknown_datatype_size));
 		STARPU_ASSERT_MSG(ret == NM_ESUCCESS, "nm_sr_recv_peek returned %d", ret);
 
-		req->ptr = malloc(req->count);
+		req->ptr = (void *)starpu_malloc_on_node_flags(STARPU_MAIN_RAM, req->count, 0);
 		STARPU_ASSERT_MSG(req->ptr, "cannot allocate message of size %ld", req->count);
 
 		nm_mpi_nmad_data_get(&(req->backend->unknown_datatype_body), (void*) req->ptr, req->datatype, req->count);