agx_batch_cleanup: Assertion `bo->writer_syncobj == batch->syncobj' failed

I may have been too hasty merging the syncobj change. With Chromium + WebGL, I was able to hit this assertion. I don't have a great reproducer for this yet. (I think it was with Aquarium. Otherwise would have been get.webgl.org. Nothing fancy, was just smoketesting.) This is the Chromium build in Fedora, on top of agx/next (i.e. gl3 renderer).

chromium-browser: ../src/gallium/drivers/asahi/agx_batch.c:341: agx_batch_cleanup: Assertion bo->writer_syncobj == batch->syncobj' failed.`