TLS 1.3: Use selected key exchange mode field

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index aeaeb3d..c306d3c 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -1237,7 +1237,7 @@
      * client_handshake_traffic_secret and server_handshake_traffic_secret
      * are derived in the handshake secret derivation stage.
      */
-    if( mbedtls_ssl_tls13_some_ephemeral_enabled( ssl ) )
+    if( mbedtls_ssl_tls13_key_exchange_mode_with_ephemeral( ssl ) )
     {
         if( mbedtls_ssl_tls13_named_group_is_ecdhe( handshake->offered_group_id ) )
         {