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_gettime.c

@@ -81,7 +81,7 @@ int timer_gettime(timer_t timerid, FAR struct itimerspec *value)
 
   /* Get the number of ticks before the underlying watchdog expires */
 
-  ticks = wd_gettime(timer->pt_wdog);
+  ticks = wd_gettime(&timer->pt_wdog);
 
   /* Convert that to a struct timespec and return it */