Bluetooth: HCI request error handling

When we are building a HCI request with more than one HCI command
and one of the hci_req_add calls fail, we should have some cleanup
routine so the HCI commands already queued on HCI request can be
deleted. Otherwise, we will face some memory leaks issues.

This patch implements the HCI request error handling which is the
following: If a hci_req_add fails, we save the error code in hci_
request. Once hci_req_run is called, we verify the error field. If
it is different from zero, we delete all HCI commands already queued
and return the error code.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>