drm/syncobj: add missing error return code in drm_syncobj_transfer_to_timeline()

If dma_fence_unwrap_merge() fails, it should return error code
in drm_syncobj_transfer_to_timeline()

Fixes: ec8d985ff26f ("drm: use dma_fence_unwrap_merge() in drm_syncobj")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Yang Yingliang <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Christian König <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_syncobj.c

···
 
 	fence = dma_fence_unwrap_merge(tmp);
 	dma_fence_put(tmp);
-	if (!fence)
+	if (!fence) {
+		ret = -ENOMEM;
 		goto err_put_timeline;
+	}
 
 	chain = dma_fence_chain_alloc();
 	if (!chain) {