rtc alarm:fix doesn't call nxsig_notification

Signed-off-by: yangguangcai <yangguangcai@xiaomi.com>

drivers/timers/rtc.c

@@ -185,15 +185,15 @@ static void rtc_alarm_callback(FAR void *priv, int alarmid)
 
   if (alarminfo->active)
     {
+      /* The alarm is no longer active */
+
+      alarminfo->active = false;
+
       /* Yes.. signal the alarm expiration */
 
       nxsig_notification(alarminfo->pid, &alarminfo->event,
                          SI_QUEUE, &alarminfo->work);
     }
-
-  /* The alarm is no longer active */
-
-  alarminfo->active = false;
 }
 #endif