Bluetooth: Make hci-destruct callback optional

Several drivers already provide an empty callback so we can actually
make this optional and then remove all those empty callbacks in the
drivers.

This callback isn't needed at all by most drivers as they can remove
their allocated structures on device disconnect and not on hci
destruction.

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>

include/net/bluetooth/hci_core.h

@@ -595,8 +595,10 @@ static inline void hci_conn_put(struct hci_conn *conn)
 /* ----- HCI Devices ----- */
 static inline void __hci_dev_put(struct hci_dev *d)
 {
-	if (atomic_dec_and_test(&d->refcnt))
-		d->destruct(d);
+	if (atomic_dec_and_test(&d->refcnt)) {
+		if (d->destruct)
+			d->destruct(d);
+	}
 }
 
 /*

net/bluetooth/hci_core.c

@@ -1551,7 +1551,7 @@ int hci_register_dev(struct hci_dev *hdev)
 	BT_DBG("%p name %s bus %d owner %p", hdev, hdev->name,
 						hdev->bus, hdev->owner);
 
-	if (!hdev->open || !hdev->close || !hdev->destruct)
+	if (!hdev->open || !hdev->close)
 		return -EINVAL;
 
 	/* Do not allow HCI_AMP devices to register at index 0,