tests/sched_policies/data_locality.c: make the cost function return 1.0 instead of 0.0.

The point of this cost function is to prevent the scheduler from using a greedy
approach. If must therefore return a value __strictly__ greater than 0.

tests/sched_policies/data_locality.c

@@ -29,7 +29,7 @@ cost_function(struct starpu_task *task, unsigned nimpl)
 {
 	(void) task;
 	(void) nimpl;
-	return 0.0;
+	return 1.0;
 }
 
 static struct starpu_perfmodel model =