Bluetooth: Remove HCI-owner field

After unregistering an hci_dev object a bluetooth driver does not have
any callbacks in the hci_dev structure left over. Therefore, there is no
need to keep a reference to the module.

Previously, we needed this to protect the hci-destruct callback.
However, this callback is no longer available so we do not need this
owner field, anymore.  Drivers now call hci_unregister_dev() and they
are done with the object.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>