Fix use of C style cast.

Fix use of C style cast.

Fix the test tst_Moc::oldStyleCasts()

(The test make sure moc do not generate old C cast, by compiling the
generated code and testing for gcc warning. But if it is present in the
public header, the warning will be shown)

Change-Id: I2fd3d01e7d78639d97bea021c200afbe2caae85f
Reviewed-on: http://codereview.qt.nokia.com/1772
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>