xprtrdma: Use ro_unmap_sync in xprt_rdma_send_request

The "safe" version of ro_unmap is used here to avoid waiting
unnecessarily. However:

 - It is safe to wait. After all, we have to wait anyway when using
   FMR to register memory.

 - This case is rare: it occurs only after a reconnect.

By switching this call site to ro_unmap_sync, the final use of
ro_unmap_safe is removed.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/transport.c

@@ -728,7 +728,8 @@ xprt_rdma_send_request(struct rpc_task *task)
 
 	/* On retransmit, remove any previously registered chunks */
 	if (unlikely(!list_empty(&req->rl_registered)))
-		r_xprt->rx_ia.ri_ops->ro_unmap_safe(r_xprt, req, false);
+		r_xprt->rx_ia.ri_ops->ro_unmap_sync(r_xprt,
+						    &req->rl_registered);
 
 	rc = rpcrdma_marshal_req(r_xprt, rqst);
 	if (rc < 0)