Fix compilation of qmlviewer

"qmlruntime.cpp:123: error: invalid use of incomplete type"
 'const struct QMimeData'"

Change-Id: I427fee401e9fa7cd658c3d01e7530720141e4fa0
Reviewed-on: http://codereview.qt-project.org/5786


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kent Hansen <kent.hansen@nokia.com>