The ADCCONTROL4 and DACCONTROL1 registers are similar but not identical,
with the DACCONTROL1 having each field starting one bit higher than
ADCCONTROL4.

Instead of introducing a magic shift, add new constants for the values
in ADCCONTROL4 and use a second variable to setup the ADC.
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Mark Brown <broonie@kernel.org>