drm/amdgpu: correct the cu and rb info for sienna cichlid

Skip disabled sa to correct the cu_info and active_rbs for sienna cichlid.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 5.9.x