fix generate check fail

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/scripts/generate_ssl_debug_helpers.py b/scripts/generate_ssl_debug_helpers.py
index ad1f949..fb72690 100755
--- a/scripts/generate_ssl_debug_helpers.py
+++ b/scripts/generate_ssl_debug_helpers.py
@@ -322,7 +322,7 @@
     parser.add_argument('--mbedtls-root', nargs='?', default=build_tree.guess_mbedtls_root(),
                         help='root directory of mbedtls source code')
     parser.add_argument('output_directory', nargs='?',
-                        default=sys.stdout, help='source/header files location')
+                        default='library', help='source/header files location')
 
     args = parser.parse_args()