iio: iio_buffer_register: Use correct channel when calculating masklength

The channel set assigned to the iio device is not necessarily the same has the
channel set passed to iio_buffer_register. So to avoid possible complications
always work with the channel set pass to iio_buffer_register and ignore the
channel set assigned to the iio device.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -292,7 +292,7 @@ int iio_buffer_register(struct iio_dev *indio_dev,
 			if (channels[i].scan_index >
 			    (int)indio_dev->masklength - 1)
 				indio_dev->masklength
-					= indio_dev->channels[i].scan_index + 1;
+					= channels[i].scan_index + 1;
 
 			ret = iio_buffer_add_channel_sysfs(indio_dev,
 							 &channels[i]);