[ofw] Add Assert to debug BS while deleting WDF device

[Hefty, Sean]

> > It's SM 3.3.6 if I understand correctly it uses winmad
> 
> That is correct.

Given the details so far, it seems unlikely that the ControlDevice is the actual issue.  It must be valid if opensm is using it.  It seems more likely there's something wrong in the device removal handling code.  I'll continue to look at the code in this area to see what the issue might be.

- Sean