tty_port: Fix refcounting leak in tty_port_tty_hangup()

tty_port: Fix refcounting leak in tty_port_tty_hangup()

The function tty_port_tty_hangup() could leak a reference to the tty_struct:

        struct tty_struct *tty = tty_port_tty_get(port);

        if (tty && (!check_clocal || !C_CLOCAL(tty))) {
                tty_hangup(tty);
                tty_kref_put(tty);
        }

If tty != NULL and the second condition is false we never call tty_kref_put and
the reference is leaked.

Fix by always calling tty_kref_put() which accepts a NULL argument.

The patch fixes a regression introduced by commit aa27a094.

Acked-by: Gustavo Padovan <[email protected]>
Signed-off-by: Gianluca Anzolin <[email protected]>
Acked-by: Jiri Slaby <[email protected]>
Cc: stable <[email protected]> # 3.10
Signed-off-by: Greg Kroah-Hartman <[email protected]>