SwVirtFlyDrawObj: suppress unused parameter warnings (it's used by assert)

Change-Id: I2f5b530e011bf1bb95ca5e0421f6e03c0885872a
(cherry picked from commit 39669d3244e3859471e665cf6afc754b6aca634e)
Signed-off-by: Eike Rathke <erack@redhat.com>