dt-bindings: hwmon: Add the +vs supply to the lm75 bindings

Some boards might have a regulator that control the +VS supply, add it
to the bindings.

Signed-off-by: Alban Bedel <alban.bedel@aerq.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201001145738.17326-3-alban.bedel@aerq.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>