IB/mlx4: Fix use of flow-counters for process_mad

For IB links, reading HCA flow counters through iboe_process_mad() should
be used when mlx4_ib_process_mad() is invoked only for VFs PMA queries and
exactly nothing else.

Fixes: 7193a141

 ('IB/mlx4: Set VF to read from QP counters')
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>