regulator: tps65218: fix DCDC4 linear voltage range

The second range of this particular regulator,
starts at 1.60V, not as 1.55V as it was originally
implied by code.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org