drm/amdgpu: remove job->adev (v2)

We can get that from the ring.

v2: squash in "drm/amdgpu: always initialize job->base.sched" (Alex)

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>