qapi: Simplify gen_visit_fields() error handling

Since we have consolidated all generated code to use 'err' as
the name of the local variable for error detection, we can
simplify the decision on whether to skip error detection (useful
for deallocation paths) to be a boolean.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1443565276-4535-18-git-send-email-eblake@redhat.com>
[Change to gen_visit_fields() simplified]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index 9d214a6..43a893b 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -101,19 +101,17 @@
         return ret
 
     if dealloc:
-        errarg = None
         ret += mcgen('''
     qmp_input_visitor_cleanup(qiv);
     qdv = qapi_dealloc_visitor_new();
     v = qapi_dealloc_get_visitor(qdv);
 ''')
     else:
-        errarg = 'err'
         ret += mcgen('''
     v = qmp_input_get_visitor(qiv);
 ''')
 
-    ret += gen_visit_fields(arg_type.members, errarg=errarg)
+    ret += gen_visit_fields(arg_type.members, skiperr=dealloc)
 
     if dealloc:
         ret += mcgen('''