[update][kernel]规范rt_object_t强制转换的使用，消除上次提交的编译警告

src/timer.c

@@ -201,7 +201,7 @@ void rt_timer_init(rt_timer_t  timer,
     RT_ASSERT(timer != RT_NULL);
 
     /* timer object initialization */
-    rt_object_init((rt_object_t)timer, RT_Object_Class_Timer, name);
+    rt_object_init(&(timer->parent), RT_Object_Class_Timer, name);
 
     _rt_timer_init(timer, timeout, parameter, time, flag);
 }
@@ -298,7 +298,7 @@ rt_err_t rt_timer_delete(rt_timer_t timer)
     /* enable interrupt */
     rt_hw_interrupt_enable(level);
 
-    rt_object_delete((rt_object_t)timer);
+    rt_object_delete(&(timer->parent));
 
     return RT_EOK;
 }