regulator: use linear_ranges helper

Change the regulator helpers to use common linear_ranges code.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Link: https://lore.kernel.org/r/64f01d5e381b8631a271616b7790f9d5640974fb.1588944082.git.matti.vaittinen@fi.rohmeurope.com


Signed-off-by: Mark Brown <broonie@kernel.org>