Bluetooth: btusb: Remove device lock on release

Recently we changed the way how we release driver-data. A driver is now
responsible of destroying the data so we no longer need the device lock
on deinitialization in btusb driver.

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>