Fixed the compilation error of HeltecV4Board::begin.

variants/heltec_v4/HeltecV4Board.cpp

@@ -10,6 +10,7 @@ void HeltecV4Board::begin() {
     loRaFEMControl.init();
 
     periph_power.begin();
+    esp_reset_reason_t reason = esp_reset_reason();
     if (reason == ESP_RST_DEEPSLEEP) {
       long wakeup_source = esp_sleep_get_ext1_wakeup_status();
       if (wakeup_source & (1 << P_LORA_DIO_1)) {  // received a LoRa packet (while in deep sleep)