iio: st_sensors: Fix buffer copy

Use byte_for_channel as iterator to properly initialize the buffer.
Signed-off-by: Robin van der Gracht <robin@protonic.nl>
Acked-by: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: <Stable@vger.kernel.org>

drivers/iio/common/st_sensors/st_sensors_buffer.c

@@ -71,7 +71,7 @@ int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 				goto st_sensors_free_memory;
 			}
 
-			for (i = 0; i < n * num_data_channels; i++) {
+			for (i = 0; i < n * byte_for_channel; i++) {
 				if (i < n)
 					buf[i] = rx_array[i];
 				else