[turbofan] Fix register constraint for memory barrier.

test/mjsunit/regress/regress-590074.js

+// Copyright 2016 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 --expose-gc
+
+var __v_5 = {};
+
+function __f_10() {
+  var __v_2 = [0, 0, 0];
+  __v_2[0] = 0;
+  gc();
+  return __v_2;
+}
+
+function __f_2(array) {
+  array[1] = undefined;
+}
+
+function __f_9() {
+  var __v_4 = __f_10();
+  __f_2(__f_10());
+  __v_5 = __f_10();
+  __v_4 = __f_10();
+  __f_2(__v_5);
+}
+__f_9();
+%OptimizeFunctionOnNextCall(__f_9);
+__f_9();