sched/wdog: Don't dynamically allocate wdog_s

to save the preserved space(1KB) and also avoid the heap overhead

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: I694073f68e1bd63960cedeea1ddec441437be025

sched/timer/timer.h

@@ -55,7 +55,7 @@ struct posix_timer_s
   pid_t            pt_owner;       /* Creator of timer */
   int              pt_delay;       /* If non-zero, used to reset repetitive timers */
   int              pt_last;        /* Last value used to set watchdog */
-  WDOG_ID          pt_wdog;        /* The watchdog that provides the timing */
+  struct wdog_s    pt_wdog;        /* The watchdog that provides the timing */
   struct sigevent  pt_event;       /* Notification information */
   struct sigwork_s pt_work;
 };