drm/amdgpu: Correct xgmi_wafl block name

Fix backward compatibility issue to stay with
the old name of xgmi_wafl node.

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