Fix warning

Summary:
Can't assign an edge to an anchor

file:///home/apol/devel/kde5/lib64/qml/org/kde/kirigami/styles/Desktop/OverlayDrawer.qml:115:23: Unable to assign int to QQuickAnchorLine
file:///home/apol/devel/kde5/lib64/qml/org/kde/kirigami/styles/Desktop/OverlayDrawer.qml:116:24: Unable to assign int to QQuickAnchorLine

Test Plan: There's no such warning anymore

Reviewers: Kirigami, mart

Reviewed By: mart

Subscribers: plasma-devel

Tags: Kirigami

Differential Revision: https://phabricator.kde.org/D2517