regulator: tps6287x: Fix missing .n_voltages setting

Otherwise, regulator_list_voltage() will return -EINVAL.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20230516082333.466429-1-axel.lin@ingics.com


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