port_xmit_data is written instead of port_rcv_data.

Fixes: 3efd9a11 ('IB/mlx5: Modify MAD reading counters method to use counter registers')
Signed-off-by: NTalat Batheesh <talatb@mellanox.com>
Signed-off-by: NLeon Romanovsky <leon@kernel.org>
Signed-off-by: NDoug Ledford <dledford@redhat.com>