rpcserver: fix make lint

rpcserver.go

@@ -1997,8 +1997,8 @@ out:
 			// If a final channel open update is being sent, then
 			// we can break out of our recv loop as we no longer
 			// need to process any further updates.
-			switch update := fundingUpdate.Update.(type) {
-			case *lnrpc.OpenStatusUpdate_ChanOpen:
+			update, ok := fundingUpdate.Update.(*lnrpc.OpenStatusUpdate_ChanOpen)
+			if ok {
 				chanPoint := update.ChanOpen.ChannelPoint
 				txid, err := GetChanPointFundingTxid(chanPoint)
 				if err != nil {