iio: accel: adxl367: Fix alignment for DMA safety

____cacheline_aligned is insufficient guarantee for non-coherent DMA.
Switch to the updated IIO_DMA_MINALIGN definition.

Update comment to reflect that DMA safety may require separate
cachelines.

Fixes: cbab791c ("iio: accel: add ADXL367 driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Cosmin Tanislav <demonsingur@gmail.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220508175712.647246-5-jic23@kernel.org

drivers/iio/accel/adxl367.c

@@ -179,7 +179,7 @@ struct adxl367_state {
 	unsigned int	fifo_set_size;
 	unsigned int	fifo_watermark;
 
-	__be16		fifo_buf[ADXL367_FIFO_SIZE] ____cacheline_aligned;
+	__be16		fifo_buf[ADXL367_FIFO_SIZE] __aligned(IIO_DMA_MINALIGN);
 	__be16		sample_buf;
 	u8		act_threshold_buf[2];
 	u8		inact_time_buf[2];

drivers/iio/accel/adxl367_spi.c

@@ -9,6 +9,8 @@
 #include <linux/regmap.h>
 #include <linux/spi/spi.h>
 
+#include <linux/iio/iio.h>
+
 #include "adxl367.h"
 
 #define ADXL367_SPI_WRITE_COMMAND	0x0A
@@ -28,10 +30,10 @@ struct adxl367_spi_state {
 	struct spi_transfer	fifo_xfer[2];
 
 	/*
-	 * DMA (thus cache coherency maintenance) requires the
-	 * transfer buffers to live in their own cache lines.
+	 * DMA (thus cache coherency maintenance) may require the
+	 * transfer buffers live in their own cache lines.
 	 */
-	u8			reg_write_tx_buf[1] ____cacheline_aligned;
+	u8			reg_write_tx_buf[1] __aligned(IIO_DMA_MINALIGN);
 	u8			reg_read_tx_buf[2];
 	u8			fifo_tx_buf[1];
 };