[turbofan] Fix misplaced DCHECK

Bug: chromium:1062532
Change-Id: Iaac3103987a561ce519321276c623b5eb37ec830
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2108022
Commit-Queue: Georg Neis <neis@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66764}

src/compiler/constant-folding-reducer.cc

@@ -46,8 +46,8 @@ bool IsAlreadyBeingFolded(Node* node) {
   bool found = false;
   for (Edge edge : node->use_edges()) {
     if (!NodeProperties::IsValueEdge(edge)) continue;
-    DCHECK(!found);
     if (edge.from()->opcode() == IrOpcode::kFoldConstant) {
+      DCHECK(!found);
       found = true;
 #ifndef ENABLE_SLOW_DCHECKS
       break;