fix silly build errors

main/battery.cpp

@@ -1,4 +1,4 @@
-#include "battery.c"
+#include "battery.h"
 
 #include "driver/adc.h"
 #include "esp_adc_cal.h"
@@ -8,7 +8,7 @@ namespace gay_ipod {
 
 static esp_adc_cal_characteristics_t calibration;
 
-esp_error_t init_adc(void) {
+esp_err_t init_adc(void) {
   // Calibration should already be fused into the chip from the factory, so
   // we should only need to read it back out again.
   esp_adc_cal_characterize(

main/battery.h

@@ -1,9 +1,13 @@
 #ifndef BATTERY_H
 #define BATTERY_H
 
+#include <stdint.h>
+
+#include "esp_err.h"
+
 namespace gay_ipod {
 
-esp_error_t init_adc(void);
+esp_err_t init_adc(void);
 
 /**
  * Returns the current battery level in millivolts.

main/gay-ipod-fw.cpp

@@ -97,11 +97,11 @@ extern "C" void app_main(void)
   ESP_ERROR_CHECK(expander.Write());
 
   ESP_LOGI(TAG, "Init ADC");
-  ESP_ERROR_CHECK(init_adc());
+  ESP_ERROR_CHECK(gay_ipod::init_adc());
 
 
   while (1) {
-    uint32_t battery = read_battery_voltage();
+    uint32_t battery = gay_ipod::read_battery_voltage();
     expander.Read();
 
     ESP_LOGI(TAG, "millivolts: %d, wall power? %d", battery, expander.charge_power_ok());