fix warnings: 'XX' defined as a struct here but previously declared as a class [-Wmismatched-tags]

src/qt/addresstablemodel.cpp

@@ -27,8 +27,9 @@ struct AddressTableEntry
 };
 
 // Private implementation
-struct AddressTablePriv
+class AddressTablePriv
 {
+public:
     CWallet *wallet;
     QList<AddressTableEntry> cachedAddressTable;