dt-bindings: hwmon: convert AD AD741x bindings to dt-schema

Convert the Analog Devices AD741x bindings to dt-schema.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201117220807.208747-2-krzk@kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>