iio: potentiometer: ad5272: Fix alignment for DMA safety

iio: potentiometer: ad5272: Fix alignment for DMA safety

____cacheline_aligned is an insufficient guarantee for non-coherent DMA
on platforms with 128 byte cachelines above L1.  Switch to the updated
IIO_DMA_MINALIGN definition.

Fixes: d0d863bfa9ea ("iio: ad5272: Add support for Analog Devices digital potentiometers")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-82-jic23@kernel.org