iw_cxgb4: only clear the ARMED bit if a notification is needed

In __flush_qp(), the CQ ARMED bit was being cleared regardless of
whether any notification is actually needed.  This resulted in the iser
termination logic getting stuck in ib_drain_sq() because the CQ was not
marked ARMED and thus the drain CQE notification wasn't triggered.

This new bug was exposed when this commit was merged:

commit cbb40fad ("iw_cxgb4: only call the cq comp_handler when the
cq is armed")

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>