Fix crash on mergeSync

BUG=674133

Review-Url: https://codereview.chromium.org/2583823002
Cr-Commit-Position: refs/heads/master@{#439071}

components/reading_list/ios/reading_list_store.cc

@@ -235,7 +235,7 @@ syncer::SyncError ReadingListStore::MergeSyncData(
       // Write to the store.
       std::unique_ptr<reading_list::ReadingListLocal> entry_local_pb =
           merged_entry->AsReadingListLocal();
-      batch_->WriteData(entry->URL().spec(),
+      batch_->WriteData(merged_entry->URL().spec(),
                         entry_local_pb->SerializeAsString());
 
       // Send to sync