Fix middleware writer: (#343)

## Description


Func now only returns an error when the error is not nil.

## Why is this needed
logs were showing an error when there wasnt one.

```json
{"level":"error","ts":1695434959.912211,"caller":"script/ipxe.go:152","msg":"unable to write boot script","script":"auto.ipxe","error":"writing response: %!w(<nil>)","stacktrace":"github.com/tinkerbell/smee/ipxe/script.(*Handler).serveBootScript\n\t/home/tink/repos/tinkerbell/boots/ipxe/script/ipxe.go:152\ngithub.com/tinkerbell/smee/ipxe/script.(*Handler).HandlerFunc.func1\n\t/home/tink/repos/tinkerbell/boots/ipxe/script/ipxe.go:108\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2122\ngo.opentelemetry.io/contrib/instrumentation/net/http/otelhttp.WithRouteTag.func1\n\t/root/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/[email protected]/handler.go:262\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2122\nnet/http.(*ServeMux).ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2500\ngo.opentelemetry.io/contrib/instrumentation/net/http/otelhttp.(*Handler).ServeHTTP\n\t/root/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/[email protected]/handler.go:212\ngithub.com/tinkerbell/smee/ipxe/http.(*loggingMiddleware).ServeHTTP\n\t/home/tink/repos/tinkerbell/boots/ipxe/http/middleware.go:35\nnet/http.serverHandler.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2936\nnet/http.(*conn).serve\n\t/usr/local/go/src/net/http/server.go:1995"}
```


Fixes: #

## How Has This Been Tested?





## How are existing users impacted? What migration steps/scripts do we need?





## Checklist:

I have:

- [ ] updated the documentation and/or roadmap (if required)
- [ ] added unit or e2e tests
- [ ] provided instructions on how to upgrade

ipxe/http/middleware.go

@@ -49,8 +49,11 @@ func (w *responseWriter) Write(b []byte) (int, error) {
 		w.statusCode = 200
 	}
 	n, err := w.ResponseWriter.Write(b)
+	if err != nil {
+		return 0, fmt.Errorf("failed writing response: %w", err)
+	}
 
-	return n, fmt.Errorf("writing response: %w", err)
+	return n, nil
 }
 
 func (w *responseWriter) WriteHeader(code int) {