IB/mlx5: Fix port counter ID association to QP offset

The q-counter-id is given in modify-QP command associates
the QP with the counter. The offset to which the counter
ID was set is incorrect, causing IB port counters not to
count on QP.

Fixes: 0837e86a ('IB/mlx5: Add per port counters')
Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Tested-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>