drm/amdgpu: Don't show false warning for reg list

If reg list is already loaded on PSP 13.0.2 SOCs, psp will give
TEE_ERR_CANCEL response on second time load. Avoid printing warn
message for it.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>