regulator: sm5703: Fix missing n_voltages for fixed regulators

Set n_voltages = 1 for fixed regulators.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Markuss Broks <markuss.broks@gmail.com>
Link: https://lore.kernel.org/r/20230409025529.241699-1-axel.lin@ingics.com


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