Remove unnecessary function

internal/upstream/upstream.go

@@ -39,11 +39,7 @@ type Upstream struct {
 }
 
 func (u *Upstream) URLPrefix() urlprefix.Prefix {
-	u.configureURLPrefixOnce.Do(u.configureURLPrefix)
-	return u.urlPrefix
-}
-
-func (u *Upstream) configureURLPrefix() {
+	u.configureURLPrefixOnce.Do(func() {
 		if u.Backend == nil {
 			u.Backend = DefaultBackend
 		}
@@ -52,6 +48,9 @@ func (u *Upstream) configureURLPrefix() {
 			relativeURLRoot += "/"
 		}
 		u.urlPrefix = urlprefix.Prefix(relativeURLRoot)
+	})
+
+	return u.urlPrefix
 }
 
 func (u *Upstream) RoundTripper() *badgateway.RoundTripper {
@@ -61,6 +60,7 @@ func (u *Upstream) RoundTripper() *badgateway.RoundTripper {
 			ResponseHeaderTimeout: u.ResponseHeaderTimeout,
 		}
 	})
+
 	return u.roundtripper
 }