qapi: Pass file name to QAPIGen constructor instead of methods

Not much of an improvement now, but the next commit will profit.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190301154051.23317-4-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index ebf4889..6d66bf6 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -239,7 +239,7 @@
         QAPISchemaModularCVisitor.__init__(
             self, prefix, 'qapi-commands',
             ' * Schema-defined QAPI/QMP commands', __doc__)
-        self._regy = QAPIGenCCode()
+        self._regy = QAPIGenCCode(None)
         self._visited_ret_types = {}
 
     def _begin_user_module(self, name):