compat: adapt signature change of tty_flip_buffer_push() and tty_insert_flip_string()

compat: adapt signature change of tty_flip_buffer_push() and tty_insert_flip_string()

The method signature of tty_flip_buffer_push() and
tty_insert_flip_string() was changed in these commits and this converts
it to the old behavior.

commit 2e124b4a390ca85325fae75764bef92f0547fa25
Author: Jiri Slaby <jslaby@suse.cz>
Date:   Thu Jan 3 15:53:06 2013 +0100

    TTY: switch tty_flip_buffer_push

commit 05c7cd39907184328f48d3e7899f9cdd653ad336
Author: Jiri Slaby <jslaby@suse.cz>
Date:   Thu Jan 3 15:53:04 2013 +0100

    TTY: switch tty_insert_flip_string

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>