Fix texture cache invalidation...

Uhh, so this has apparently been broken for a while.  The address is intentionally in the high bits.

With the backoff off (default), we don't use this code.  It's only used with backoff on.  It definitely may have been causing graphical glitches.

This could potentially:
 * Make the backoff cache slower, hashing more often.
 * Fix glitches with backoff on without much perf hit.
 * Have almost no impact whatsoever.

I haven't really tested this and don't have time atm, but I'm worried it will just make it slower mainly.  If so, we should just remove the invalidation altogether I guess, since it's not been actually... invalidating.

-[Unknown]