iio: potentiometer: mcp41010: 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: 092cb71a ("iio: potentiometer: Add driver for Microchip MCP41xxx/42xxx")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-84-jic23@kernel.org

drivers/iio/potentiometer/mcp41010.c

@@ -60,7 +60,7 @@ struct mcp41010_data {
 	const struct mcp41010_cfg *cfg;
 	struct mutex lock; /* Protect write sequences */
 	unsigned int value[MCP41010_MAX_WIPERS]; /* Cache wiper values */
-	u8 buf[2] ____cacheline_aligned;
+	u8 buf[2] __aligned(IIO_DMA_MINALIGN);
 };
 
 #define MCP41010_CHANNEL(ch) {					\