qapi-commands: Drop useless initialization

In generated command handlers, the assignment to retval dominates its
only use.  Therefore, its initialization is useless.  Drop it.

Suggested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index cfbd59c..8bf84a7 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -205,14 +205,10 @@
                 header=hdr)
 
     if ret_type:
-        if is_c_ptr(ret_type):
-            retval = "    %s retval = NULL;" % c_type(ret_type)
-        else:
-            retval = "    %s retval;" % c_type(ret_type)
         ret += mcgen('''
-%(retval)s
+    %(c_type)s retval;
 ''',
-                     retval=retval)
+                     c_type=c_type(ret_type))
 
     if len(args) > 0:
         ret += gen_visitor_input_containers_decl(args)