iio: dac: ad5791: Fix alignment for DMA saftey

____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: 791bb52a ("iio:ad5791: Do not store transfer buffers on the stack")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-56-jic23@kernel.org

drivers/iio/dac/ad5791.c

@@ -95,7 +95,7 @@ struct ad5791_state {
 	union {
 		__be32 d32;
 		u8 d8[4];
-	} data[3] ____cacheline_aligned;
+	} data[3] __aligned(IIO_DMA_MINALIGN);
 };
 
 enum ad5791_supported_device_ids {