IB/mthca: fix for SQEr-to-RTS transition in modify QP

Fixes to SQEr->RTS transition in modify_qp:
1. The flag IB_QP_ACCESS_FLAGS is optional for UC qps
2. The SQEr state is not supported for RC qps

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>