iio: Always compute masklength

Even if no userspace consumer buffer is attached to the IIO device at
registration we still need to compute the masklength, since it is possible
that a in-kernel consumer buffer is going to get attached to the device at
a later point.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -966,6 +966,15 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
 	int ret, i, attrn, attrcount, attrcount_orig = 0;
 	const struct iio_chan_spec *channels;
 
+	channels = indio_dev->channels;
+	if (channels) {
+		int ml = indio_dev->masklength;
+
+		for (i = 0; i < indio_dev->num_channels; i++)
+			ml = max(ml, channels[i].scan_index + 1);
+		indio_dev->masklength = ml;
+	}
+
 	if (!buffer)
 		return 0;
 
@@ -1009,12 +1018,6 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
 			if (channels[i].scan_index < 0)
 				continue;
 
-			/* Establish necessary mask length */
-			if (channels[i].scan_index >
-			    (int)indio_dev->masklength - 1)
-				indio_dev->masklength
-					= channels[i].scan_index + 1;
-
 			ret = iio_buffer_add_channel_sysfs(indio_dev,
 							 &channels[i]);
 			if (ret < 0)