[rigctl] Use "fout" for consistency

This makes no difference in the current code, but other usages
of dumpconf_list() are different:
$ grep dumpconf_list *parse.c
rigctl_parse.c:        dumpconf_list(rig, stdout);
rigctl_parse.c:        dumpconf_list(rig, fout);
rotctl_parse.c:        dumpconf_list(rot, fout);
rotctl_parse.c:        dumpconf_list(rot, fout);
rotctl_parse.c:    dumpconf_list(rot, fout);

tests/rigctl_parse.c

@@ -6048,7 +6048,7 @@ declare_proto_rig(get_conf)
 
     if (arg1 == NULL || arg1[0] == '?')
     {
-        dumpconf_list(rig, stdout);
+        dumpconf_list(rig, fout);
         debugmsgsave[0] = 0;
         debugmsgsave2[0] = 0;
         return RIG_OK;