drm/scheduler: properly forward fence errors

When a hw fence is signaled with an error properly forward that to the
finished fence.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230420115752.31470-1-christian.koenig@amd.com