usb: cdc-acm: fix error handling in acm_probe()

acm_probe() ignores errors in tty_port_register_device()
and leaves intfdata pointing to freed memory on alloc_fail7
error path. The patch fixes the both issues.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>