Bluetooth: btusb: Make use of of BIT macro to declare flags

This makes use of BIT macro when declaring BTUSB flags which makes it
understand how many bits are in use and many are left.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>