pidl/tests: fix ndr_push_init_ctx() usage

pidl/tests: fix ndr_push_init_ctx() usage

The code in libndr got rid of the second argument quite some time ago
(2010): f9ca9e46ad24036bf00cb361a6cef4b2e7e98d7d

However, pidl tests did include a code that passed two arguments.
Recently GCC started to fail to compile such code.

Signed-off-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Thu Aug 30 04:48:00 CEST 2018 on sn-devel-144