Staging: ipack/devices/ipoctal: Get rid of ipoctal_list.

Use tty_dev->dev's drdata to associate struct ipocal_channel to the
respective tty_struct.

Signed-off-by: Jens Taprogge <jens.taprogge@taprogge.org>
Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>