tests/microbenchs/prefetch_data_on_node.c: add missing unregister

tests/microbenchs/prefetch_data_on_node.c

@@ -136,6 +136,7 @@ int main(int argc, char **argv)
 	ret = starpu_task_wait_for_all();
 	STARPU_CHECK_RETURN_VALUE(ret, "starpu_task_wait_for_all");
 
+	starpu_data_unregister(v_handle);
 	starpu_free(v);
 	starpu_shutdown();