[serializer] fix hash function for hashmap used for serializing.

Yes. I thought I was being smart. And yes. It's just a one-liner.

TBR=cbruni@chromium.org
BUG=chromium:672009

Review-Url: https://codereview.chromium.org/2555213005
Cr-Commit-Position: refs/heads/master@{#41572}

src/address-map.h

@@ -38,9 +38,7 @@ class PointerToIndexHashMap
     return reinterpret_cast<uintptr_t>(value);
   }
 
-  static uint32_t Hash(uintptr_t key) {
-    return static_cast<uint32_t>(key >> kPointerSizeLog2);
-  }
+  static uint32_t Hash(uintptr_t key) { return static_cast<uint32_t>(key); }
 };
 
 class AddressToIndexHashMap : public PointerToIndexHashMap<Address> {};