Make sure the device has at least 2 completion vectors
before allocating to compvec#1

Fixes: a4699f56 (xprtrdma: Put Send CQ in IB_POLL_WORKQUEUE mode)
Signed-off-by: NNicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>
Reviewed-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>