iio: frequency: admv4420: 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: b59c0415 ("iio: frequency: admv4420.c: Add support for ADMV4420")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-71-jic23@kernel.org

drivers/iio/frequency/admv4420.c

@@ -113,7 +113,7 @@ struct admv4420_state {
 	struct admv4420_n_counter	n_counter;
 	enum admv4420_mux_sel		mux_sel;
 	struct mutex			lock;
-	u8				transf_buf[4] ____cacheline_aligned;
+	u8				transf_buf[4] __aligned(IIO_DMA_MINALIGN);
 };
 
 static const struct regmap_config admv4420_regmap_config = {