drm/amdgpu: replace mmhub_funcs with mmhub.funcs

remove mmhub_funcs in adev

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>