iio: dac: ad5593r: add check for i2c functionality

Make sure that the needed i2c functionality is supported during probe.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20220913073413.140475-3-nuno.sa@analog.com


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