regulator: rt6160: Convert to use regulator_set_ramp_delay_regmap

Use regulator_set_ramp_delay_regmap instead of open-coded.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210603093809.1108629-1-axel.lin@ingics.com


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