[S390] 3270: do not register with tty_register_device

The tty3270_notifier that calls tty_register_device / tty_unregister_device
is harmful in two ways:
1) the device node that is create is wrong because the minor numbers for
   3270 tty start with 1 and tty_notifier passes the minor as index.
2) If 1) is corrected you'll get a warning:
     WARNING: at fs/sysfs/dir.c:462 sysfs_add_one+0x4c/0x60()
     sysfs: duplicate filename '227:1' can not be created
   The 227:1 link is already created by raw3270_create_attributes to refer
   to ../../class/tty/tty<devno>. There cannot be two links.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>