RDMA/hw/hfi1/rc: Demote incorrectly populated kernel-doc header

RDMA/hw/hfi1/rc: Demote incorrectly populated kernel-doc header

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

 drivers/infiniband/hw/hfi1/rc.c:1388: warning: Function parameter or member 'packet' not described in 'hfi1_send_rc_ack'
 drivers/infiniband/hw/hfi1/rc.c:1388: warning: Function parameter or member 'is_fecn' not described in 'hfi1_send_rc_ack'
 drivers/infiniband/hw/hfi1/rc.c:1388: warning: Excess function parameter 'qp' description in 'hfi1_send_rc_ack'

Link: https://lore.kernel.org/r/20210126124732.3320971-21-lee.jones@linaro.org
Cc: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
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>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>