drm/amdgpu/mmhub_v1: bypass clockgating setting

For SRIOV doesn't need CG, so bypass it.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>