regulator: as3722: Fix off-by-one n_voltages setting for SDx

AS3722_SDx_VSEL_MAX means the maximum selecter, the n_voltages should be
AS3722_SDx_VSEL_MAX + 1.

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