drm/amdgpu: rename fence->scheduler to sched v2

Just to be consistent with the other members.

v2: rename the ring member as well.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com> (v1)
Reviewed-by: Chunming <Zhou&lt;david1.zhou@amd.com>