QNX: Use window group of top-level window for mmr

Pass the top-level window's window group to mm-renderer,
as required by mmr.

Change-Id: I2a2e8b4aa48f5c2292b03593c6d528068f383b5c
Reviewed-by: Bernd Weimer <bweimer@blackberry.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>