Bluetooth: hci_ll: Use skb_put_u8 instead of struct hcill_cmd

The struct hcill_cmd to create an skb with a single u8 is pointless. So
just use skb_put_u8 instead.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>