USB Camera: Use vendor/product, not serial, like pretixPRINT, to avoid permission issues

[raphaelm]

No description provided.

[robbi5]

Integer.toHexString results in vendor/device-ids with missing leading zeros, thats why we have pretix/pretixprint-android#63 open in pretixPRINT.
Maybe we want to go here directly with ${String.format("%04x", device.vendorId)}:${String.format("%04x", device.productId)} :)