regulator: max20411: Fix off-by-one for n_voltages setting

Otherwise regulator_list_voltage returns -EINVAL for MAX20411_MAX_SEL.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20230211150019.1545542-1-axel.lin@ingics.com


Signed-off-by: Mark Brown <broonie@kernel.org>