iio: mcp320x: Fix occasional incorrect readings

Without the cacheline alignment, the readings will occasionally incorrectly
return 0.

Signed-off-by: Michael Welling <mwelling@ieee.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/mcp320x.c

@@ -60,12 +60,12 @@ struct mcp320x {
 	struct spi_message msg;
 	struct spi_transfer transfer[2];
 
-	u8 tx_buf;
-	u8 rx_buf[2];
-
 	struct regulator *reg;
 	struct mutex lock;
 	const struct mcp320x_chip_info *chip_info;
+
+	u8 tx_buf ____cacheline_aligned;
+	u8 rx_buf[2];
 };
 
 static int mcp320x_channel_to_tx_data(int device_index,