Bluetooth: Don't clear the blacklist when closing the HCI device

Clearing the blacklist in hci_dev_do_close() would mean that user space
needs to do extra work to re-block devices after a DEVDOWN-DEVUP cycle.
This patch removes the clearing of the blacklist in this case and
thereby saves user space from the extra work.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Acked-by: Ville Tervo <ville.tervo@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>