iio: accel: adxl367: Fix alignment for DMA safety

____cacheline_aligned is insufficient guarantee for non-coherent DMA.
Switch to the updated IIO_DMA_MINALIGN definition.

Update comment to reflect that DMA safety may require separate
cachelines.

Fixes: cbab791c ("iio: accel: add ADXL367 driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Cosmin Tanislav <demonsingur@gmail.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-5-jic23@kernel.org