sim: igen: update options API

This local macro doesn't take any args, so adjust the API to match.
No one really noticed as this is behind code that is not normally
built, only when a dev specifically tries to compile it.

sim/igen/gen.c

@@ -1643,7 +1643,7 @@ main (int argc, char **argv)
     error (NULL,
 	   "Usage: insn <filter-in> <hi-bit-nr> <insn-bit-size> <widths> <decode-table> <insn-table>\n");
 
-  INIT_OPTIONS (options);
+  INIT_OPTIONS ();
 
   filter_parse (&options.flags_filter, argv[1]);