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

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

Changeset c804af2c1d31 ("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: c804af2c1d31 ("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.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>