iio: adc: qcom-spmi-adc5: add ADC5_VREF_VADC to rev2 ADC5

Add support for ADC5_VREF_VADC channel to rev2 ADC5 channel list.
This channel measures the VADC reference LDO output.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Link: https://lore.kernel.org/r/20220818221815.346233-3-robimarko@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>