staging:iio:cdc:ad7150: Drop unnecessary block comments.

These have a habit of not getting updated with driver reorganizations
and don't add much info so drop them.

Also fix a minor comment syntax issue.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210314181511.531414-17-jic23@kernel.org