drm/amdgpu: move mmhub ras fini to mmhub block

it's more suitable to put mmhub ras fini in mmhub block

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