[turbofan] Fix missing machine type for float32/float64 array accesses.

test/mjsunit/asm/float64array-store-div.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.
+
+function Module(stdlib, foreign, heap) {
+  "use asm";
+  var MEM64 = new stdlib.Float64Array(heap);
+  function foo(i) {
+    MEM64[0] = (i >>> 0) / 2;
+    return MEM64[0];
+  }
+  return { foo: foo };
+}
+
+var foo = Module(this, {}, new ArrayBuffer(64 * 1024)).foo;
+assertEquals(0.5, foo(1));