Bluetooth: Correctly acquire module ref

We provide a device-object to other subsystems and we provide our own
release-function. Therefore, the device-object must own a reference to
our module, otherwise the release-function may get deleted before the
device-object does.

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>