QNX: Evaluate mm-renderer buffer status

In the playing (or paused) state the media status should reflect the
buffer state, it should not stay in the loaded media state.

Mm-renderer differentiates between buffer "status" and "level".
Unfortunately, QMediaPlayer's buffer status maps to mm-renderer's
buffer level.

Change-Id: I22ea8dc83cee975fc4aa1a6de4f172def042a9a8
QT-BUG: 37166
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>