iio: dac: ad5764: Fix alignment for DMA safety

iio: dac: ad5764: Fix alignment for DMA safety

[ Upstream commit b378722a3e9bb51318c0de7eeb4d71f2fcd6987f ]

____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.

Update the comment to include 'may'.

Fixes: 68b14d7ea956 ("staging:iio:dac: Add AD5764 driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-53-jic23@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>