iio: adc: ad7923: Fix buffer overflow for tx_buf and ring_xfer

The AD7923 was updated to support devices with 8 channels, but the size
of tx_buf and ring_xfer was not increased accordingly, leading to a
potential buffer overflow in ad7923_update_scan_mode().

Fixes: 851644a ("iio: adc: ad7923: Add support for the ad7908/ad7918/ad7928")
Cc: stable@vger.kernel.org
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Zicheng Qu <quzicheng@huawei.com>
Link: https://patch.msgid.link/20241029134637.2261336-1-quzicheng@huawei.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: nunojsa

drivers/iio/adc/ad7923.c

@@ -48,7 +48,7 @@
 
 struct ad7923_state {
 	struct spi_device		*spi;
-	struct spi_transfer		ring_xfer[5];
+	struct spi_transfer		ring_xfer[9];
 	struct spi_transfer		scan_single_xfer[2];
 	struct spi_message		ring_msg;
 	struct spi_message		scan_single_msg;
@@ -64,7 +64,7 @@ struct ad7923_state {
 	 * Length = 8 channels + 4 extra for 8 byte timestamp
 	 */
 	__be16				rx_buf[12] __aligned(IIO_DMA_MINALIGN);
-	__be16				tx_buf[4];
+	__be16				tx_buf[8];
 };
 
 struct ad7923_chip_info {