fix pointer incoherency

mpi/src/starpu_mpi_cache.c

@@ -92,7 +92,7 @@ void _starpu_mpi_cache_shutdown()
 	STARPU_PTHREAD_MUTEX_LOCK(&_cache_mutex);
 	HASH_ITER(hh, _cache_data, entry, tmp)
 	{
-		struct _starpu_mpi_data *mpi_data = entry->data_handle;
+		struct _starpu_mpi_data *mpi_data = entry->data_handle->mpi_data;
 		free(mpi_data->cache_sent);
 		mpi_data->cache_sent = NULL;
 		HASH_DEL(_cache_data, entry);