IB/mthca: Simplify CQ cleaning in mthca_free_qp()

mthca_free_qp() already has local variables to hold the QP's send_cq
and recv_cq, so we can slightly clean up the calls to mthca_cq_clean()
by using those local variables instead of expressions like
to_mcq(qp->ibqp.send_cq).

Also, by cleaning the recv_cq first, we can avoid worrying about
whether the QP is attached to an SRQ for the second call, because we
would only clean send_cq if send_cq is not equal to recv_cq, and that
means send_cq cannot have any receive completions from the QP being
destroyed.

All this work even improves the generated code a bit:

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-5 (-5)
function                                     old     new   delta
mthca_free_qp                                510     505      -5
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_qp.c

@@ -1419,11 +1419,10 @@ void mthca_free_qp(struct mthca_dev *dev,
 	 * unref the mem-free tables and free the QPN in our table.
 	 */
 	if (!qp->ibqp.uobject) {
-		mthca_cq_clean(dev, to_mcq(qp->ibqp.send_cq), qp->qpn,
-			       qp->ibqp.srq ? to_msrq(qp->ibqp.srq) : NULL);
-		if (qp->ibqp.send_cq != qp->ibqp.recv_cq)
-			mthca_cq_clean(dev, to_mcq(qp->ibqp.recv_cq), qp->qpn,
+		mthca_cq_clean(dev, recv_cq, qp->qpn,
 			       qp->ibqp.srq ? to_msrq(qp->ibqp.srq) : NULL);
+		if (send_cq != recv_cq)
+			mthca_cq_clean(dev, send_cq, qp->qpn, NULL);
 
 		mthca_free_memfree(dev, qp);
 		mthca_free_wqe_buf(dev, qp);