avoid using deprecated field

examples/perf_steering/perf_knobs_03.c

@@ -116,7 +116,7 @@ int main(int argc, char **argv)
 		STARPU_ASSERT(starpu_perf_knob_get_type_id(id) == starpu_perf_knob_type_name_to_id(knob_type_name));
 
 		struct starpu_codelet cl = {
-			.cpu_func = cpu_func
+			.cpu_funcs = {cpu_func}
 		};
 
 		task_count[0] = 0;