[turbofan] Fix undefined behavior in accessing operator parameters

OpParameter<int32_t> was still used for an operator after the operators
parameter changed from int32_t to a struct. Coincidentally, the first
field of the struct holds the value previously stored in that int32_t,
so correctness tests did not catch this.

Bug: chromium:818611, v8:7517
Change-Id: Ie46f084f7fa8117cd3493fc5ceafac11553dc55e
Reviewed-on: https://chromium-review.googlesource.com/948546
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51728}

src/compiler/verifier.cc

@@ -298,8 +298,8 @@ void Verifier::Visitor::Check(Node* node, const AllNodes& all) {
           case IrOpcode::kIfValue: {
             for (const Node* user : node->uses()) {
               if (user != use && user->opcode() == IrOpcode::kIfValue) {
-                CHECK_NE(OpParameter<int32_t>(use->op()),
-                         OpParameter<int32_t>(user->op()));
+                CHECK_NE(IfValueParametersOf(use->op()).value(),
+                         IfValueParametersOf(user->op()).value());
               }
             }
             ++count_case;