TTY: isdn, define tty_port_operations

Add there .carrier_raised. It is taken from current block_til_ready.
We will need tty_port->ops->carrier_raised for
tty_port_block_til_ready helper.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>