iio: humidity: hts211: Use devm_regulator_get_enable()

This driver only turns the power on at probe and off via a custom
devm_add_action_or_reset() callback. The new devm_regulator_get_enable()
replaces this boilerplate code.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20221016163409.320197-10-jic23@kernel.org