[kcm/effects] Clip ListView

Summary:
Otherwise the content overflows the frame when scrolling.

QQC2 scrollview docs say "ScrollView does not automatically clip its contents. If it is not used as a full-screen item, you should consider setting the clip property to true"

Test Plan:
Before:
{F8121150}

After:
{F8121152}

Reviewers: #kwin, #plasma, ngraham

Reviewed By: ngraham

Subscribers: ngraham, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D27558

kcmkwin/kwineffects/package/contents/ui/main.qml

@@ -86,6 +86,8 @@ ScrollViewKCM {
 
         property var _buttonGroups: []
 
+        clip: true
+
         model: Private.EffectsFilterProxyModel {
             id: searchModel