anv: Fix the target_bo assertion in anv_reloc_list_add

Fixes: b75a92e2010e "anv: assert that the target bo is valid..."
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3528
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6759>
1 file changed