iio: amplifiers: ad8366: 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.

Update the comment to include 'may'.

Fixes: e71d42e03c ("iio: amplifiers: New driver for AD8366 Dual-Digital Variable Gain Amplifier")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-42-jic23@kernel.org

drivers/iio/amplifiers/ad8366.c

@@ -45,10 +45,10 @@ struct ad8366_state {
 	enum ad8366_type	type;
 	struct ad8366_info	*info;
 	/*
-	 * DMA (thus cache coherency maintenance) requires the
+	 * DMA (thus cache coherency maintenance) may require the
 	 * transfer buffers to live in their own cache lines.
 	 */
-	unsigned char		data[2] ____cacheline_aligned;
+	unsigned char		data[2] __aligned(IIO_DMA_MINALIGN);
 };
 
 static struct ad8366_info ad8366_infos[] = {