net/mlx5: Fix typo in mlx5_query_port_pvlc

We used the wrong register name for querying the PVLC register

Fixes: a124d13e

 ('net/mlx5_core: Add more query port helpers')
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>