staging: iio: ad7746: White space cleanup

Tidy up some trivial whitespace issues.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220626122938.582107-15-jic23@kernel.org