libceph: fix doc warnings in cls_lock_client.c

Add description to fix the following W=1 kernel build warnings:

 net/ceph/cls_lock_client.c:28: warning: Function parameter or
  member 'osdc' not described in 'ceph_cls_lock'
 net/ceph/cls_lock_client.c:28: warning: Function parameter or
  member 'oid' not described in 'ceph_cls_lock'
 net/ceph/cls_lock_client.c:28: warning: Function parameter or
  member 'oloc' not described in 'ceph_cls_lock'

[ idryomov: tweak osdc description ]

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>