[turbofan] Fix deopt for assignments in non-effect context.

test/mjsunit/regress/regress-assignment-in-test-context.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --always-opt
+// Flags: --turbo-filter=* --turbo-deoptimization
+
+function assertEquals() {}
+
+function f(o) {
+  if (o.setterProperty = 0) {
+    return 1;
+  }
+  return 2;
+}
+
+function deopt() { %DeoptimizeFunction(f); }
+
+assertEquals(2,
+             f(Object.defineProperty({}, "setterProperty", { set: deopt })));