staging: iio: ad2s1210: fix 'assignment operator' style checks

This patch fixes all "Assignment operator '=' should be on the previous
line" checks found in ad2s1210.c with checkpatch.pl.

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>