dt-bindings: iio: ad74413r: allow setting sink current for digital input

Depending on the actual hardware wired up to a digital input channel,
it may be necessary to configure the ad74413r to sink a small
current. For example, in the case of a simple mechanical switch, the
charge on the external 68 nF capacitor (cf. the data sheet's Figure
34) will keep the channel as reading high even after the switch is
turned off again.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230306094301.1357543-2-linux@rasmusvillemoes.dk


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