regulator: Fix voltage range selection

Use the correct field to fix wrong voltage range selection on regulators
such as tps6287x since the blamed commit.

Fixes: 269cb04b

 ("regulator: Use bitfield values for range selectors")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20230911-regulator-voltage-sel-v1-1-886eb1ade8d8@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>