optimize rbtree initialization and insert
diff --git a/src/event/ngx_event_timer.c b/src/event/ngx_event_timer.c
index 589de6d..2931a9f 100644
--- a/src/event/ngx_event_timer.c
+++ b/src/event/ngx_event_timer.c
@@ -26,9 +26,8 @@
 ngx_int_t
 ngx_event_timer_init(ngx_log_t *log)
 {
-    ngx_event_timer_rbtree.root = &ngx_event_timer_sentinel;
-    ngx_event_timer_rbtree.sentinel = &ngx_event_timer_sentinel;
-    ngx_event_timer_rbtree.insert = ngx_rbtree_insert_timer_value;
+    ngx_rbtree_init(&ngx_event_timer_rbtree, &ngx_event_timer_sentinel,
+                    ngx_rbtree_insert_timer_value);
 
 #if (NGX_THREADS)