Fix no-psk

Fixes #6239

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6253)
diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index c5f2235..354769b 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -4192,6 +4192,7 @@
     }
 
     if (SSL_IS_TLS13(s)) {
+#ifndef OPENSSL_NO_PSK
         int j;
 
         /*
@@ -4208,6 +4209,7 @@
                 prefer_sha256 = 1;
             }
         }
+#endif
     } else {
         tls1_set_cert_validity(s);
         ssl_set_masks(s);