dt-bindings: iio: adc: maxim,max9611 yaml conversions

Straight forward conversion of this binding for this
current sense amplifier and ADC.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Rob Herring <robh@kernel.org>