iio: adc: ad7280a: 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: 003f1d48 ("staging:iio:adc:ad7280a: Split buff[2] into tx and rx parts")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-11-jic23@kernel.org

drivers/iio/adc/ad7280a.c

@@ -183,7 +183,7 @@ struct ad7280_state {
 	unsigned char			cb_mask[AD7280A_MAX_CHAIN];
 	struct mutex			lock; /* protect sensor state */
 
-	__be32				tx ____cacheline_aligned;
+	__be32				tx __aligned(IIO_DMA_MINALIGN);
 	__be32				rx;
 };