Bluetooth: Fix returning proper cmd_complete for mgmt_block/unblock

The Block/Unblock Device Management commands should return Command
Complete instead of Command Status whenever possible so that user space
can distinguish exactly which command failed in the case of multiple
commands. This patch does the necessary changes in the command handler
to return the right event to user space.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>