Notifier: properly reset HAL alarm in non-periodic case (#1296)

The loop spins otherwise.

wpilibc/src/main/native/include/frc/Notifier.h

@@ -88,6 +88,13 @@ class Notifier : public ErrorBase {
  private:
   /**
    * Update the HAL alarm time.
+   *
+   * @param triggerTime the time at which the next alarm will be triggered
+   */
+  void UpdateAlarm(uint64_t triggerTime);
+
+  /**
+   * Update the HAL alarm time based on m_expirationTime.
    */
   void UpdateAlarm();