drm/amdgpu: not return error on the init_apu_flags

In some APU project we needn't always assign flags to identify each other,
so we may not need return an error.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>