tls13: srv: replace with internal API to check is_tls12_enabled

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index b3f25b5..eb0b528 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1921,7 +1921,7 @@
      */
     if (SSL_CLIENT_HELLO_TLS1_2 == parse_client_hello_ret) {
         /* Check if server supports TLS 1.2 */
-        if (ssl->conf->min_tls_version > MBEDTLS_SSL_VERSION_TLS1_2) {
+        if (!mbedtls_ssl_conf_is_tls12_enabled(ssl->conf)) {
             MBEDTLS_SSL_DEBUG_MSG(
                 1, ("Unsupported version of TLS 1.2 was received"));
             MBEDTLS_SSL_PEND_FATAL_ALERT(