TTY: ttyprintk, initialize tty_port earlier

After tty_register_driver is called, it is too late to initialize a
guy with which we operate in open. When a process already called
open(2) on that node, the structures may be in use uninitialized.

Move the initialization prior to tty_register_driver.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Samo Pogacnik <samo_pogacnik@t-2.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>