drm/nouveau/kms/nv50-: Fix drm_dp_remove_payload() invocation

We changed the semantics for this in:

commit e761cc20 ("drm/display/dp_mst: Handle old/new payload states in
drm_dp_remove_payload()")

But I totally forgot to update this properly in nouveau. So, let's do that.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613210529.552098-1-lyude@redhat.com

drivers/gpu/drm/nouveau/dispnv50/disp.c

@@ -909,15 +909,19 @@ nv50_msto_prepare(struct drm_atomic_state *state,
 	struct nouveau_drm *drm = nouveau_drm(msto->encoder.dev);
 	struct nv50_mstc *mstc = msto->mstc;
 	struct nv50_mstm *mstm = mstc->mstm;
-	struct drm_dp_mst_atomic_payload *payload;
+	struct drm_dp_mst_topology_state *old_mst_state;
+	struct drm_dp_mst_atomic_payload *payload, *old_payload;
 
 	NV_ATOMIC(drm, "%s: msto prepare\n", msto->encoder.name);
 
+	old_mst_state = drm_atomic_get_old_mst_topology_state(state, mgr);
+
 	payload = drm_atomic_get_mst_payload_state(mst_state, mstc->port);
+	old_payload = drm_atomic_get_mst_payload_state(old_mst_state, mstc->port);
 
 	// TODO: Figure out if we want to do a better job of handling VCPI allocation failures here?
 	if (msto->disabled) {
-		drm_dp_remove_payload(mgr, mst_state, payload, payload);
+		drm_dp_remove_payload(mgr, mst_state, old_payload, payload);
 
 		nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index, 0, 0, 0, 0);
 	} else {