Use path() as we need the path without the filename

On Windows, filePath() was used for a function that was supposed to get
the bin directory for Qt. However path() should be used instead as this
will remove the filename from the originally obtained string.

Change-Id: I16f8bda91fe9666c935318f8d73c715d2ea908f5
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>