TreeModel: Rows are not columns.

Change-Id: I33a6d017f14ee9703b374f645c279cc26e3cb3e5
Reviewed-by: hjk <hjk121@nokiamail.com>

src/libs/utils/treemodel.cpp

@@ -186,7 +186,7 @@ int TreeModel::columnCount(const QModelIndex &idx) const
 {
     checkIndex(idx);
     if (!idx.isValid())
-        return m_root->rowCount();
+        return m_root->columnCount();
     if (idx.column() > 0)
         return 0;
     return itemFromIndex(idx)->columnCount();