drm/amdgpu: Remove clock gating restore.

Restoring clock gating break SMU opeartion afterwards, avoid
this until this further invistigated with SMU.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-and-tested-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>