dt-bindings: iio: mlx90632 Add supply regulator documentation

Document the newly added vdd supply option.

Signed-off-by: Crt Mori <cmo@melexis.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220808144936.1559158-1-cmo@melexis.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>