intel/aub: Actually run BLT batches on the blit ring.

We didn't set the ring flag for BLT batches, so they got run on the
render ring.  Shenanigans ensued, especially when we sent commands that
were only valid on the BLT ring.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>