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

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 <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220613063454.2609364-1-yangyingliang@huawei.com