manual_reduction: only enable needed workers

src/core/workers.c

@@ -1159,6 +1159,7 @@ int starpu_conf_noworker(struct starpu_conf *conf)
 	conf->nopencl = 0;
 	conf->nmic = 0;
 	conf->nmpi_ms = 0;
+	return 0;
 }
 
 static void _starpu_conf_set_value_against_environment(char *name, int *value, int precedence_over_env)

tests/datawizard/manual_reduction.c

@@ -206,8 +206,10 @@ int main(int argc, char **argv)
 	struct starpu_conf conf;
 
 	starpu_conf_init(&conf);
-	conf.nmic = 0;
-	conf.nmpi_ms = 0;
+	starpu_conf_noworker(&conf);
+	conf.ncpus = -1;
+	conf.ncuda = -1;
+	conf.nopencl = -1;
 
 	variable = INIT_VALUE;