drm/amdgpu:fix the check in cs_ib_fill for SRIOV

1,the check is only appliable for SRIOV GFX engine.
2,use chunk_ib instead of ib.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Ken Wang <Qingqing.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>