tty: xtensa/iss, don't reassign to tty->port

tty: xtensa/iss, don't reassign to tty->port

We already do tty_port_link_device in rs_init, so we don't need to
reassign a port to tty->port. It would be too late in tty::ops::open
anyway.

Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: linux-xtensa@linux-xtensa.org
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-30-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>