rg_input: use the unit parameter instead of RG_BATTERY_ADC_UNIT in the legacy ADC path

[koalaauto]

Summary

_adc_setup_channel() takes an adc_unit_t unit parameter, but its legacy branch tests the battery macro RG_BATTERY_ADC_UNIT instead of that parameter. As a result any target that does not define RG_BATTERY_ADC_UNIT fails to compile.

Details

components/retro-go/rg_input.c:

static inline bool _adc_setup_channel(adc_unit_t unit, adc_channel_t channel, adc_atten_t atten, bool calibrate)
{
    RG_ASSERT(unit == ADC_UNIT_1 || unit == ADC_UNIT_2, "Invalid ADC unit");
    esp_err_t err = ESP_FAIL;
#ifdef USE_ADC_DRIVER_NG
    ...                                     // uses `unit` correctly
#else
    if (RG_BATTERY_ADC_UNIT == ADC_UNIT_1)  // <-- should be `unit`
    {
        adc1_config_width(ADC_WIDTH_MAX - 1);
        err = adc1_config_channel_atten(channel, atten);
    }
    else if (RG_BATTERY_ADC_UNIT == ADC_UNIT_2)  // <-- should be `unit`
    {
        err = adc2_config_channel_atten(channel, atten);
    }
#endif
    if (err != ESP_OK)
    {
        RG_LOGE("Failed to configure ADC_UNIT_%d channel:%d atten:%d error:0x%02X",
                (int)unit, ...);            // already uses `unit`

Two things make this bite:

1. USE_ADC_DRIVER_NG is commented out at the top of the file (// #define USE_ADC_DRIVER_NG), so the #else branch is the one actually compiled.
2. The function is static inline, so its body is compiled even when nothing calls it.

Consequently a target with, say, RG_GAMEPAD_ADC_MAP but no battery ADC — or simply no RG_BATTERY_* defines at all — dies with:

rg_input.c:71:9: error: 'RG_BATTERY_ADC_UNIT' undeclared (first use in this function);
                        did you mean 'RG_BATTERY_CALC_VOLTAGE'?

The intent is clearly to use the parameter: the very next RG_LOGE() already prints (int)unit, and the RG_ASSERT at the top validates unit.

Fix

Use unit in the legacy branch, matching the USE_ADC_DRIVER_NG branch and the assert/log around it.

Testing

Found while porting a new 160x128 ESP32 target that has no battery ADC. Before the change it would not compile on dev; after it builds and runs (ESP-IDF v5.5.2, release build) with both the gamepad and battery paths behaving as before on targets that do define RG_BATTERY_ADC_UNIT (for those, unit is exactly what was being passed in anyway).