anv: assert that the target bo is valid when adding a reloc list

this catches some undefined behavior like e.g., using a stale descriptorset
that references deleted bos, which I would absolutely never do

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6747>
1 file changed