drm/amdgpu: No longer insert ras blocks into ras_list if it already exists in ras_list

No longer insert ras blocks into ras_list if it already exists in ras_list.

Signed-off-by: yipechai <YiPeng.Chai@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>