Bluetooth: hci_qca: Remove duplicate power off in proto close

During serdev unregister, hdev->shutdown is called before
proto close. Removing duplicates power OFF call.

Signed-off-by: Venkata Lakshmi Narayana Gubba <gubbaven@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>