iio:buffer: Free active scan mask in iio_disable_all_buffers()

Usually the active scan mask is freed in __iio_update_buffers() when the buffer
is disabled. But when the device is still sampling when it is removed we'll end
up disabling the buffers in iio_disable_all_buffers(). So we also need to free
the active scan mask here, otherwise it will be leaked.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -477,6 +477,9 @@ void iio_disable_all_buffers(struct iio_dev *indio_dev)
 	indio_dev->currentmode = INDIO_DIRECT_MODE;
 	if (indio_dev->setup_ops->postdisable)
 		indio_dev->setup_ops->postdisable(indio_dev);
+
+	if (indio_dev->available_scan_masks == NULL)
+		kfree(indio_dev->active_scan_mask);
 }
 
 int iio_update_buffers(struct iio_dev *indio_dev,