[drivers]修复定时器驱动框架单次长时间定时不准确的问题

components/drivers/hwtimer/hwtimer.c

@@ -192,14 +192,15 @@ static rt_size_t rt_hwtimer_write(struct rt_device *dev, rt_off_t pos, const voi
     if (size != sizeof(rt_hwtimerval_t))
         return 0;
 
+    timer->ops->stop(timer);
+    timer->overflow = 0;
+
+    t = timeout_calc(timer, (rt_hwtimerval_t*)buffer);
     if ((timer->cycles <= 1) && (timer->mode == HWTIMER_MODE_ONESHOT))
     {
         opm = HWTIMER_MODE_ONESHOT;
     }
-    timer->ops->stop(timer);
-    timer->overflow = 0;
 
-    t = timeout_calc(timer, (rt_hwtimerval_t*)buffer);
     if (timer->ops->start(timer, t, opm) != RT_EOK)
         size = 0;