Fixing Issue #2243. Main problems were:

- HAL_ADC_GetState(adcHandle) may return other bits set (not only
  HAL_ADC_STATE_EOC_REG) when called - so I AND-ed it out as proposed by
  mattbrejza in Issue #2243.
- ADC Pin has to be configured as GPIO_MODE_ANALOG_ADC_CONTROL not only
  GPIO_MODE_ANALOG.
- Resolved ADC resolution L4 specific (Use L4 define ADC_RESOLUTION_12B).
- Changed setting of Init.EOCSelection toADC_EOC_SINGLE_CONV for L4.
- Added call to ADC_MultiModeTypeDef as this is done on a STM32Cube
  generated project too.
- Clean up: Configuration of ADC is done only in ONE function not the same
  is done in two functions.

Test is done on PA5 pin of STM32L4Discovery-Kit which is connected to the
DOWN button.

Thanks to mattbrejza for discovering the bug.