RDMA/cxgb3: Don't zero QP attrs when moving to IDLE

QP attributes must stay initialized when moving back to IDLE.  Zeroing
them will crash the system in _flush_qp() if the QP is subsequently
moved to ERROR and back to IDLE.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>