panfrost: Don't segfault on unknown models
If we don't recognize the model, dev->model will be NULL. In that case, we can't dereference dev->model to get the tilebuffer size. If we do, we'll segfault, instead of gracefully refusing to probe and loading the swrast instead.
Fixes: 96d65b47 ("panfrost: Use implementation-specific tile size") Signed-off-by: Alyssa Rosenzweig alyssa@collabora.com