SurfaceComposerClient BLAST: Avoid recaching buffers.

cacheBuffers works like this:
 1. Look for any State with eBufferChanged
 2. If it has a cache entry clear eBufferChanged and set the cache
 3. If it doesn't have an entry leave eBufferChanged set, but also set
    the cache so we can use it next time.
In the third case where we don't clear eBufferChanged we might attempt
to recache buffers that have already been cached. This might happen
in the wrong process.

Bug: 153561718
Test: Existing tests pass. BLAST Sync Engine manual test.
Change-Id: Ibe02e76d40fedef46a2418587e28e598d6e2c614