Fix non-compiling QtQml code snippet

Task-number: QTBUG-42006
Change-Id: I3c59b0ba27518750cba667f414f58edaa136d250
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Screen attached property: expose devicePixelRatio property

Change-Id: I08b22766b3e389b7d27ca4c56729f550b0647a08
Reviewed-by: Jens Bache-Wiig <jensbw@gmail.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>