regulator: fan53880: Fix missing n_voltages setting

Fixes: e6dea51e

 ("regulator: fan53880: Add initial support")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Christoph Fritz <chf.fritz@googlemail.com>
Link: https://lore.kernel.org/r/20210517105325.1227393-1-axel.lin@ingics.com
Signed-off-by: Mark Brown <broonie@kernel.org>