Bluetooth: Free potentially unfreed SCO connection

It is possible to initiate a SCO connection while deleting the
corresponding ACL connection, e.g. in below scenario:

(1) < hci setup sync connect command
(2) > hci disconn complete event (for the acl connection)
(3) > hci command complete event (for(1), failure)

When it happens, hci_cs_setup_sync_conn won't be able to obtain the
reference to the SCO connection, so it will be stuck and potentially
hinder subsequent connections to the same device.

This patch prevents that by also deleting the SCO connection if it is
still not established when the corresponding ACL connection is deleted.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Ying Hsu <yinghsu@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>