applets/mediacontroller: make artist label font size smaller

(cherry picked from commit f9a39dc4)

applets/mediacontroller/contents/ui/CompactRepresentation.qml

@@ -135,6 +135,7 @@ MouseArea {
                     visible: root.artist
 
                     elide: Text.ElideRight
+                    font.pointSize: PlasmaCore.Theme.smallestFont.pointSize
                     maximumLineCount: 1
                     text: root.artist
                     textFormat: Text.PlainText