net/mlx5_core: Fix wrong name in struct

The name refers to syndrome so uset ext_synd instread of ext_sync.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>