staging:iio:cdc:ad7150: use swapped reads/writes for i2c rather than open coding

Reduces boilerplate and chances of getting the error handling wrong.
No functional change.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon>
Link: https://lore.kernel.org/r/20210314181511.531414-2-jic23@kernel.org