dt-bindings:iio:humidity:st,hts221 yaml conversion.

Straight forward conversion of this temperature and pressure sensor binding.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20201031134110.724233-4-jic23@kernel.org