tty: don't crash in tty_init_dev when missing tty_port

tty: don't crash in tty_init_dev when missing tty_port

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>