pack_cis: Add return statement to new_tuple()

It looks like the right variable used to end up in the return register
(and still does at -O0), but let's not depend on that!
diff --git a/yacc_cis.y b/yacc_cis.y
index 4d97913..9896445 100644
--- a/yacc_cis.y
+++ b/yacc_cis.y
@@ -393,6 +393,7 @@
     t->type = type;
     t->parse = parse;
     t->next = NULL;
+    return t;
 }
 
 void yyerror(const char *msg, ...)