drm/radeon/kms: further spread spectrum fixes

Adjust modeset ordering to fix spread spectrum.
The spread spectrum command table relies on the
crtc routing to already be set in order to work
properly on some asics.

Should fix fdo bug 25741.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>