IB/srpt: docs: add a description for cq_size member

Changeset c804af2c ("IB/srpt: use new shared CQ mechanism")
added a new member for struct srpt_rdma_ch, but didn't add the
corresponding kernel-doc markup, as repoted when doing
"make htmldocs":

	./drivers/infiniband/ulp/srpt/ib_srpt.h:331: warning: Function parameter or member 'cq_size' not described in 'srpt_rdma_ch'

Add a description for it.

Fixes: c804af2c ("IB/srpt: use new shared CQ mechanism")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/df0e5f0e866b91724299ef569a2da8115e48c0cf.1603791716.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

drivers/infiniband/ulp/srpt/ib_srpt.h

@@ -256,6 +256,7 @@ enum rdma_ch_state {
  * @rdma_cm:	   See below.
  * @rdma_cm.cm_id: RDMA CM ID associated with the channel.
  * @cq:            IB completion queue for this channel.
+ * @cq_size:	   Number of CQEs in @cq.
  * @zw_cqe:	   Zero-length write CQE.
  * @rcu:           RCU head.
  * @kref:	   kref for this channel.