iw_cxgb4: Make function read_tcb() static

Fixes the following sparse warning:

drivers/infiniband/hw/cxgb4/cm.c:658:6: warning:
 symbol 'read_tcb' was not declared. Should it be static?

Fixes: 11a27e21 ("iw_cxgb4: complete the cached SRQ buffers")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Raju Rangoju <rajur@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/cxgb4/cm.c

@@ -655,7 +655,7 @@ static int send_halfclose(struct c4iw_ep *ep)
 	return c4iw_l2t_send(&ep->com.dev->rdev, skb, ep->l2t);
 }
 
-void read_tcb(struct c4iw_ep *ep)
+static void read_tcb(struct c4iw_ep *ep)
 {
 	struct sk_buff *skb;
 	struct cpl_get_tcb *req;