staging: iio: ad7746: Fix multiple line dereference

Clear checkpatch.pl WARNING about multiple line derefence but creates a
new one of line over 80 characters. In my opinion, it improves
readability.

Signed-off-by: Hernán Gonzalez <hernan@vanguardiasur.com.ar>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>