iio: ad74413r: wire up support for drive-strength-microamp property

Use the value specified in the channel configuration node to populate
the DIN_SINK field of the DIN_CONFIGx register.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20230306094301.1357543-3-linux@rasmusvillemoes.dk


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