QNX: Fix a dangling pointer use in QBluetoothServiceDiscoveryAgent on QNX

toUtf8 returns a temporary, we must not use a pointer inside it without making
sure that the QByteArray returned sticks around.

Change-Id: I4566d14f52acac083433dfe63c64365d119bbd17
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>