[kernel]补充endif后缀注释

src/clock.c

@@ -24,7 +24,7 @@
 #define rt_tick rt_cpu_index(0)->tick
 #else
 static volatile rt_tick_t rt_tick = 0;
-#endif
+#endif /* RT_USING_SMP */
 
 /**
  * @addtogroup Clock
@@ -72,7 +72,7 @@ void rt_tick_increase(void)
     rt_cpu_self()->tick ++;
 #else
     ++ rt_tick;
-#endif
+#endif /* RT_USING_SMP */
 
     /* check time slice */
     thread = rt_thread_self();
@@ -138,7 +138,7 @@ RT_WEAK rt_tick_t rt_tick_get_millisecond(void)
     #warning "rt-thread cannot provide a correct 1ms-based tick any longer,\
     please redefine this function in another file by using a high-precision hard-timer."
     return 0;
-#endif
+#endif /* 1000 % RT_TICK_PER_SECOND == 0u */
 }
 
 /**@}*/