svcrdma: Clean up locking

There's no need to protect llist_entry() with a spin lock.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/xprtrdma/svc_rdma_sendto.c

@@ -201,10 +201,11 @@ struct svc_rdma_send_ctxt *svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma)
 
 	spin_lock(&rdma->sc_send_lock);
 	node = llist_del_first(&rdma->sc_send_ctxts);
+	spin_unlock(&rdma->sc_send_lock);
 	if (!node)
 		goto out_empty;
+
 	ctxt = llist_entry(node, struct svc_rdma_send_ctxt, sc_node);
-	spin_unlock(&rdma->sc_send_lock);
 
 out:
 	rpcrdma_set_xdrlen(&ctxt->sc_hdrbuf, 0);
@@ -217,7 +218,6 @@ struct svc_rdma_send_ctxt *svc_rdma_send_ctxt_get(struct svcxprt_rdma *rdma)
 	return ctxt;
 
 out_empty:
-	spin_unlock(&rdma->sc_send_lock);
 	ctxt = svc_rdma_send_ctxt_alloc(rdma);
 	if (!ctxt)
 		return NULL;