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: Talat Batheesh <talatb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>