Set correct output buffer type in vidioc_dqbuf

When userspace dequeues an output buffer from the driver, that buffer should
have type V4L2_BUF_TYPE_VIDEO_OUTPUT. Previously we were providing the type
from our internal buffer which is V4L2_BUF_TYPE_VIDEO_CAPTURE.

v4l2loopback.c

@@ -1553,6 +1553,7 @@ static int vidioc_dqbuf(struct file *file, void *private_data, struct v4l2_buffe
 		dprintkrw("output DQBUF index: %d\n", b->buffer.index);
 		unset_flags(b);
 		*buf = b->buffer;
+		buf->type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
 		return 0;
 	default:
 		return -EINVAL;