Use proper types when calling qBound.

qBound is a template function defined as:

 const T &qBound (const T &min, const T &value, const T &max )

On ARM, for some reason the type of min and max in this expression
resolves to double, and compiler fails to find a function matching
qBound(double, qreal, double). For that reason we typecast constants
to qreal explicitly.