drm/sched: Keep s_fence->parent pointer

For later driver's reference to see if the fence is signaled.

v2: Move parent fence put to resubmit jobs.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1555599624-12285-4-git-send-email-andrey.grodzovsky@amd.com