Bluetooth: Fix Marvell driver to use skb_put and hci_opcode_pack

The Marvell driver has some weird quirks on how to construct proper SKBs
with Bluetooth HCI commands. Fix it to use skb_put properly and also
use hci_opcode_pack instead of self-crafted macro.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>