Fix systemd service file generation for cross-compiling

In case of cross-compiling, the qdbus version reported from qpath only provides the path to the host's qdbus executable. For the binary that is provided on the target, no path is available with the present information. For simplicity hardcode the qdbus path for this case. If every a cross-compiled system emerges with non-standard /usr/bin/qtdbus making this path settible via a build parameter might make sense.

Signed-off-by: Andreas Cord-Landwehr cordlandwehr@kde.org