The scratch register should be accessed through MMIO instead of RLCG
in SRIOV, since it being used in RLCG register access function.

Fixes: d54762cc ("drm/amdgpu: nuke dynamic gfx scratch reg allocation")
Signed-off-by: NZhenGuo Yin <zhenguo.yin@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>