regulator: bd718x7: Use rohm generic restricted voltage setting

Use common restricted voltage setting instead of implementing own.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/5a0ee14852802690241568a29ed19ff9550b0b08.1637233864.git.matti.vaittinen@fi.rohmeurope.com


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