drm/amdgpu: return new seq_no for amd_sched_push_job

It is clean to update last_queued_v_seq in the scheduler module

Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>