server/tftpd: fix compiler warning

Follow-up from 369ce38ac1d
Reported-by: Marc Hörsken
diff --git a/tests/server/tftpd.c b/tests/server/tftpd.c
index 46b09b5..0c0e9be 100644
--- a/tests/server/tftpd.c
+++ b/tests/server/tftpd.c
@@ -709,7 +709,7 @@
       logmsg("getsockname() failed with error: (%d) %s",
              error, strerror(error));
       sclose(sock);
-      return CURL_SOCKET_BAD;
+      goto tftpd_cleanup;
     }
     switch(localaddr.sa.sa_family) {
     case AF_INET: