CVE-2025-38387 RDMA/mlx5: Initialize obj_event->obj_sub_list before xa_insert

In the Linux kernel, the following vulnerability has been resolved: RDMA/mlx5: Initialize objevent-objsublist before xainsert The objevent may be loaded immediately after inserted, then if the listhead is not initialized then we may get a poisonous pointer. This fixes the crash below: mlx5core...