regulator: da903x: Convert da9034 ldo12 to use linear ranges

The voltage table of da9034 LDO12 is:
1700000, 1750000, 1800000, 1850000, 1900000, 1950000, 2000000, 2050000
2700000, 2750000, 2800000, 2850000, 2900000, 2950000, 3000000, 3050000

The voltage table is composed of two linear ranges:
for selector 0 ... 7:
        volt = 1700000 + 50000 * selector
for selector: 8 ... 15:
        volt = 2700000 + 50000 * (selector - 8)

This patch converts da9034 LDO12 to use newly introduced helpers for multiple
linear ranges.

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