regulator: scmi: Fix off-by-one for linear regulators .n_voltages setting

For linear regulators, the .n_voltages is (max_uv - min_uv) / uv_step + 1.

Fixes: 0fbeae70 ("regulator: add SCMI driver")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20210521073020.1944981-1-axel.lin@ingics.com


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