iio: adis162xx: fix low-power docs & reports

All current ADIS162XX drivers have incorrect values defined via comments.
Also, when an error is reported the printed value is incorrect.

The functionality itself isn't affected, so it's not a critical issue.

And since the change is trivial, it was included in a single patch that
fixes these in one go. All values were correlated with the ones specified
in the data-sheets.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>