freedreno/a6xx: Fix framebuffer_barrier crash

This is emitting cmdstream, it should take the submit lock to (a) ensure we actually have a batch, and (b) prevent it from being flushed from under it. This was overlooked in the conversion.

Fixes: 02298ed1 ("freedreno: Add submit lock") Signed-off-by: Rob Clark robdclark@chromium.org