Fix invalid argument enumeration when there are >=3 arguments

This bug had no impact since currently no macro has more than 2 arguments.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/mbedtls_dev/macro_collector.py b/scripts/mbedtls_dev/macro_collector.py
index 218a718..3cad2a3 100644
--- a/scripts/mbedtls_dev/macro_collector.py
+++ b/scripts/mbedtls_dev/macro_collector.py
@@ -186,7 +186,7 @@
                 for value in argument_lists[i][1:]:
                     arguments[i] = value
                     yield self._format_arguments(name, arguments)
-                arguments[i] = argument_lists[0][0]
+                arguments[i] = argument_lists[i][0]
         except BaseException as e:
             raise Exception('distribute_arguments({})'.format(name)) from e