iio: potentiometer: ad5272: 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: 79e8a32d ("iio: ad5272: Add support for Analog Devices digital potentiometers")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-82-jic23@kernel.org

drivers/iio/potentiometer/ad5272.c

@@ -50,7 +50,7 @@ struct ad5272_data {
 	struct i2c_client       *client;
 	struct mutex            lock;
 	const struct ad5272_cfg *cfg;
-	u8                      buf[2] ____cacheline_aligned;
+	u8                      buf[2] __aligned(IIO_DMA_MINALIGN);
 };
 
 static const struct iio_chan_spec ad5272_channel = {