regulator: twl6030: Use regulator_list_voltage_linear_range for twl6030ldo_ops

Use linear range to replace the twl6030ldo_list_voltage implementation.
With this change, the min_mV is not used and can be removed from
struct twlreg_info.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>