cxgb4: Add missing annotation for service_ofldq()

Sparse reports a warning at service_ofldq()

warning: context imbalance in service_ofldq() - unexpected unlock

The root cause is the missing annotation at service_ofldq()

Add the missing __must_hold(&q->sendq.lock) annotation
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/sge.c

@@ -2728,6 +2728,7 @@ static void ofldtxq_stop(struct sge_uld_txq *q, struct fw_wr_hdr *wr)
  *	is ever running at a time ...
  */
 static void service_ofldq(struct sge_uld_txq *q)
+	__must_hold(&q->sendq.lock)
 {
 	u64 *pos, *before, *end;
 	int credits;