Explicitly ignore returned value from close() in ngx_event_core_init_conf().

We don't have strong reason to inform about any errors
reported by close() call here, and there are no other things
to do with its return value.

Prodded by Coverity.

src/event/ngx_event.c

@@ -1214,7 +1214,7 @@ ngx_event_core_init_conf(ngx_cycle_t *cycle, void *conf)
     fd = epoll_create(100);
 
     if (fd != -1) {
-        close(fd);
+        (void) close(fd);
         module = &ngx_epoll_module;
 
     } else if (ngx_errno != NGX_ENOSYS) {