staging:iio:cdc:ad7150: Add scale and offset to info_mask_shared_by_type

The datasheet provides these two values on the assumption they are applied
to unshift raw value.  Hence shift both the offset and scale by 4
to compensate.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210314181511.531414-19-jic23@kernel.org