adc: mchp_xec: right justify ADC output data under 10-bit res

This enables the ADC output data to be shifted right when using
10-bit resolution. Or else, data would be left justified as if
it's doing 12-bit ADC with the right 2 bits filled with zeroes.

Fixes #23202

Signed-off-by: Daniel Leung <daniel.leung@intel.com>