For STM32L4 series, the internal sensors are connected to:
- ADC1_IN0: Internal voltage reference
- ADC1_IN17: Temperature sensor
- ADC1_IN18: VBAT battery voltage monitoring
but ADC_CHANNEL_VREFINT, ADC_CHANNEL_VBAT, ADC_CHANNEL_TEMPSENSOR are not
defined as 0, 17, 18.
This commit converts channel 0, 17, 18 to ADC_CHANNEL_x in
adc_get_internal_channel().
2154ee2163