regulator: palmas: fix number of SMPS voltages

Number of voltages for SMPS regulators was off by one.

Signed-off-by: Graeme Gregory <gg@slimlogic.co.uk>
Signed-off-by: Ian Lartey <ian@slimlogic.co.uk>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>