iio: dac: ad5770r: Fix alignment for DMA safety

iio: dac: ad5770r: 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: cbbb819837f6 ("iio: dac: ad5770r: Add AD5770R support")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Alexandru Tachici <alexandru.tachici@analog.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-55-jic23@kernel.org