IB/mthca: Fix posting >255 recv WRs for Tavor

Fix posting lists of > 255 receive WRs for Tavor: rq.next_ind must
be updated each doorbell, otherwise the next doorbell will use an
incorrect index.

Found by Ronni Zimmermann at Mellanox.
Signed-off-by: Michael S. Tsirkin <mst@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_qp.c

@@ -1862,6 +1862,7 @@ int mthca_tavor_post_receive(struct ib_qp *ibqp, struct ib_recv_wr *wr,
 				      dev->kar + MTHCA_RECEIVE_DOORBELL,
 				      MTHCA_GET_DOORBELL_LOCK(&dev->doorbell_lock));
 
+			qp->rq.next_ind = ind;
 			qp->rq.head += MTHCA_TAVOR_MAX_WQES_PER_RECV_DB;
 			size0 = 0;
 		}