Bluetooth: Force -EIO from tty read/write if .activate() fails

If rfcomm_dlc_open() fails, set tty into error state which returns
-EIO from reads and writes.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-By: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>