RDMA/hw/mlx5/qp: Demote non-conformant kernel-doc header

RDMA/hw/mlx5/qp: Demote non-conformant kernel-doc header

Fixes the following W=1 kernel build warning(s):

 drivers/infiniband/hw/mlx5/qp.c:5384: warning: Function parameter or member 'qp' not described in 'mlx5_ib_qp_set_counter'
 drivers/infiniband/hw/mlx5/qp.c:5384: warning: Function parameter or member 'counter' not described in 'mlx5_ib_qp_set_counter'

Link: https://lore.kernel.org/r/20210121094519.2044049-3-lee.jones@linaro.org
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>