iio: buffer: Fix wait_queue not being removed

commit 0642340 upstream.

In the edge case where the IIO device is unregistered while we're
buffering, we were directly returning an error without removing the wait
queue. Instead, set 'ret' and break out of the loop.

Fixes: 9eeee3b ("iio: Add output buffer support")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: nunojsa

drivers/iio/industrialio-buffer.c

@@ -228,8 +228,10 @@ static ssize_t iio_buffer_write(struct file *filp, const char __user *buf,
 	written = 0;
 	add_wait_queue(&rb->pollq, &wait);
 	do {
-		if (!indio_dev->info)
-			return -ENODEV;
+		if (!indio_dev->info) {
+			ret = -ENODEV;
+			break;
+		}
 
 		if (!iio_buffer_space_available(rb)) {
 			if (signal_pending(current)) {