ML: fix typo (fix missing vtable)

modules/gui/qt4/components/playlist/ml_model.cpp

@@ -259,7 +259,7 @@ int MLModel::getId( QModelIndex index ) const
     return getItem( index )->id();
 }
 
-QVariant MLModel::data( const QModelIndex &index, int role ) const
+QVariant MLModel::data( const QModelIndex &index, const int role ) const
 {
     if( index.isValid() )
     {

modules/gui/qt4/components/playlist/ml_model.hpp

@@ -62,7 +62,7 @@ public:
     }
     virtual int getId( QModelIndex index ) const;
 
-    QVariant data( const QModelIndex &idx, int role = Qt::DisplayRole ) const;
+    QVariant data( const QModelIndex &idx, const int role = Qt::DisplayRole ) const;
     bool setData( const QModelIndex &idx, const QVariant &value,
                   int role = Qt::EditRole );
     ml_select_e columnType( int column ) const;