Bluetooth: Fix mgmt error code for negative PIN response

The NOT_PAIRED status is only really suitable for operations where being
paired is a pre-requisite. Using it e.g. for the mgmt_pair_device
command seems unintuitive. In the case that either the local or the
remote user responds with a negative PIN Code response the "PIN or Key
Missing" HCI status will be generated. This patch changes the mapping of
this status from the NOT_PAIRED mgmt status to the more intuitive
AUTH_FAILED mgmt status.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>