media: vb2: set owner before calling vb2_read

Before vb2_read is called, the owner must be set since vb2_read will
actually start streaming. If vb2_read returns an error and q->fileio is
NULL, then it failed to start streaming and the owner is set back to NULL.

When the vb2 start_streaming callback is called, it expects the owner
pointer to be set, and that wasn't the case in this particular situation.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/common/videobuf2/videobuf2-v4l2.c

@@ -1171,10 +1171,11 @@ ssize_t vb2_fop_read(struct file *file, char __user *buf,
 		return -ERESTARTSYS;
 	if (vb2_queue_is_busy(vdev->queue, file))
 		goto exit;
+	vdev->queue->owner = file->private_data;
 	err = vb2_read(vdev->queue, buf, count, ppos,
 		       file->f_flags & O_NONBLOCK);
-	if (vdev->queue->fileio)
-		vdev->queue->owner = file->private_data;
+	if (!vdev->queue->fileio)
+		vdev->queue->owner = NULL;
 exit:
 	if (lock)
 		mutex_unlock(lock);