applets/brightness: fix QML warnings
Reason for the change
There are some warnings
QQmlExpression: Expression file:///usr/share/plasma/plasmoids/org.kde.plasma.brightness/contents/ui/KeyboardColorItem.qml:26:5 depends on non-NOTIFYable properties:
KeyboardColorControl::supported
QQmlExpression: Expression file:///usr/share/plasma/plasmoids/org.kde.plasma.brightness/contents/ui/KeyboardColorItem.qml:77:21 depends on non-NOTIFYable properties:
KeyboardColorControl::enabled
QQmlExpression: Expression file:///usr/share/plasma/plasmoids/org.kde.plasma.brightness/contents/ui/KeyboardColorItem.qml:64:21 depends on non-NOTIFYable properties:
KeyboardColorControl::enabled
file:///usr/share/plasma/plasmoids/org.kde.plasma.brightness/contents/ui/KeyboardColorItem.qml:67:21: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }