RDMA/core: Fix comment for hw stats init for port == 0

When add_port() is done for port == 0, it indicates that ports hardware
counters initialization should be skipped. Reflect so in the comment.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>