iio: addac: ad74413: don't set DIN_SINK for functions other than digital input

iio: addac: ad74413: don't set DIN_SINK for functions other than digital input

Apparently, despite the name Digital Input Configuration Register, the
settings in the DIN_CONFIGx registers also affect other channel
functions. In particular, setting a non-zero value in the DIN_SINK
field breaks the resistance measurement function.

Now, one can of course argue that specifying a drive-strength-microamp
property along with a adi,ch-func which is not one of the digital
input functions is a bug in the device tree. However, we have a rather
complicated setup with instances of ad74412r on external hardware
modules, and have set a default drive-strength-microamp in our DT
fragments describing those, merely modifying the adi,ch-func settings
to reflect however the modules have been wired up. And restricting
this setting to just being done for digital input doesn't make the
driver any more complex.

Fixes: 504eb485589d1 (iio: ad74413r: wire up support for drive-strength-microamp property)
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20230503105042.453755-1-linux@rasmusvillemoes.dk
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>