workqueue: Replace hardcoding of -20 and 19 with MIN_NICE and MAX_NICE

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/6d85138180c00ce86975addab6e34b24b84f00a5.1392103744.git.yangds.fnst@cn.fujitsu.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/workqueue.c

@@ -3225,7 +3225,7 @@ static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
 		return -ENOMEM;
 
 	if (sscanf(buf, "%d", &attrs->nice) == 1 &&
-	    attrs->nice >= -20 && attrs->nice <= 19)
+	    attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
 		ret = apply_workqueue_attrs(wq, attrs);
 	else
 		ret = -EINVAL;