Fix readonly property not respected
Fix readonly property not respected

Task-id: QTCOMPONENTS-721

drgvond/qtquickcontrols,mizukusak/qtquickcontrols,richardmg/qtcomponents,jfaust/qtquickcontrols,kobolabs/qtquickcontrols,kobolabs/qtquickcontrols,richardmg/qtcomponents,richardmg/qtcomponents,mizukusak/qtquickcontrols,jfaust/qtquickcontrols,drgvond/qtquickcontrols,kobolabs/qtquickcontrols,mizukusak/qtquickcontrols,jfaust/qtquickcontrols,drgvond/qtquickcontrols