TTY: pdc_cons, use tty_port

TTY: pdc_cons, use tty_port

Instead of digging a tty out of the tty_driver struct, which is not
defined to work, use tty_port properly. This includes proper tty
refcounting even though there is no possible race currently. But we
will need tty_port for tty buffers in the future anyway.

Signed-off-by: Jiri Slaby <[email protected]>
Cc: Kyle McMartin <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>