Like all other ST sensors, hts221 devices have VDD power line.
Introduce VDD voltage regulator to control it.
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/6b3347e78f4f920c48eb6a66936d3b69cb9ff53a.1606045688.git.lorenzo@kernel.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>