powerpc: hv{cs, si}_close() both unsigned hp->count and hvcsd->open_count cannot be negative

[Alan Cox]

> Also, I don't see why those changes have anything to do with "unsigned
> things cannot be negative".  As long as those counts are never zero on
> entry to those code sections, the existing code is fine, and I believe
> that assertion can be maintained.  If you believe the code needs to
> defend against the possibility of a zero count on entry, that should
> have been explicitly stated in the patch description.

See the tty_port patches in -next - this is an argument about code which
ought eventually to go away replaced by standard helper functions.