media: sun6i-csi: add a missing return code

As pointed by smatch, there's a missing return code:

	drivers/media/platform/sunxi/sun6i-csi/sun6i_video.c:485 sun6i_video_open() warn: missing error code 'ret'
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

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

@@ -481,8 +481,10 @@ static int sun6i_video_open(struct file *file)
 		goto fh_release;
 
 	/* check if already powered */
-	if (!v4l2_fh_is_singular_file(file))
+	if (!v4l2_fh_is_singular_file(file)) {
+		ret = -EBUSY;
 		goto unlock;
+	}
 
 	ret = sun6i_csi_set_power(video->csi, true);
 	if (ret < 0)