staging:iio:adis16400: Report correct temperature scale and offset

Temperature scale and offset differ between the different devices supported by
this driver. Right now the driver always reports the temperature scale and
offset of the adis16400 regardless of which chip variant is used. This patch
adds two new attributes to the chip_info struct, one for the temperature scale
and one for the temperature offset.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>