QFileSystemModel: reuse an existing variable

... to improve readability.

The variable 'oldName' was defined one line up from the same
expression as the RHS of the if, so use the variable instead.

Change-Id: Ifcd119317e8c9594f5280f294bc3301f681b94be
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/widgets/dialogs/qfilesystemmodel.cpp

@@ -873,7 +873,7 @@ bool QFileSystemModel::setData(const QModelIndex &idx, const QVariant &value, in
 
     QString newName = value.toString();
     QString oldName = idx.data().toString();
-    if (newName == idx.data().toString())
+    if (newName == oldName)
         return true;
 
     const QString parentPath = filePath(parent(idx));