tty: don't crash in tty_init_dev when missing tty_port

mainline inclusion
from mainline-v5.5-rc1
commit 2ae0b31e
category: bugfix
bugzilla: 82118
CVE: N/A

--------------------------------

We currently warn the user when tty->port is not set in tty_init_dev
yet. The warning says that the kernel will crash later. And it really
will only few lines below at:
tty->port->itty = tty;

So be nice and avoid the crash -- return an error instead. And update
the warning.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Link: https://lore.kernel.org/r/20191122101721.7222-1-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yi Yang <yiyang13@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>