media: platform: sunxi: sun6i-csi: fix error return code of sun6i_video_start_streaming()

When sun6i_video_remote_subdev() returns NULL to subdev, no error return
code of sun6i_video_start_streaming() is assigned.
To fix this bug, ret is assigned with -EINVAL in this case.
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Fixes: 5cc7522d ("media: sun6i: Add support for Allwinner CSI V3s")
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/sunxi/sun6i-csi/sun6i_video.c

@@ -151,8 +151,10 @@ static int sun6i_video_start_streaming(struct vb2_queue *vq, unsigned int count)
 	}
 
 	subdev = sun6i_video_remote_subdev(video, NULL);
-	if (!subdev)
+	if (!subdev) {
+		ret = -EINVAL;
 		goto stop_media_pipeline;
+	}
 
 	config.pixelformat = video->fmt.fmt.pix.pixelformat;
 	config.code = video->mbus_code;