Fixed the preliminary STM32H5 ADC support for pyb.ADC:
- Run ADC on PCLK/16.
- Use STM32 ADC library channel literals (__HAL_ADC_DECIMAL_NB_TO_CHANNEL).
- Use correct temperature conversion for H5 (30C, 130C calibration points).
Signed-off-by: Rene Straub <rene@see5.ch>