Bluetooth: Fix ERTM error reporting to the userspace

If any error occurs during transfers we have to tell userspace that
something wrong happened.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>