tradeonsi: fix preamble state producing incorrect packets

tradeonsi: fix preamble state producing incorrect packets

If the first time the preamble is written, one of the rings
isn't allocated, we wouldn't write the RING_SIZE to the preamble.

Later, when the preamble gets updated after the ring allocation,
the new RING_SIZE packet would overwrite other packets.

To prevent this, always write the RING_SIZE (the alternative would
be to write NOP packets).

This fix "*ERROR* Illegal register access in command stream" hangs
I observed on GFX8.

Fixes: 32c7805ccca ("radeonsi: merge all preamble states into one")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16962>