Don't access static functions/fields via instance

Courtesy of readability-static-accessed-through-instance

Change-Id: I71f54244f1e091315dac2943d9e1bfad6efa56a9
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/qmljseditor/qmloutlinemodel.cpp

@@ -658,7 +658,7 @@ QModelIndex QmlOutlineModel::enterFieldMemberExpression(AST::FieldMemberExpressi
     objectData.insert(AnnotationRole, QString()); // clear possible former annotation
 
     QmlOutlineItem *item = enterNode(objectData, expression, nullptr,
-                                     m_icons->functionDeclarationIcon());
+                                     Icons::functionDeclarationIcon());
 
     return item->index();
 }