Fix TLS alert codes

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 073311b..7fedf17 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1318,7 +1318,7 @@
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }