[PATCH 6/6] prime: clean up slave bo properly.

[Dave Airlie]

> This is an ABI break, in that we now pass NULL to a function
> that hasn't accepted it before.
>
> Alex Goins had a different patch for this but it wasn't symmetrical,
> it freed something in a very different place than it allocated it,
> this attempts to retain symmetry in the releasing of the backing bo.

Ignore this one for now, it isn't finished properly.

the other 5 are all good!
Dave.