usb: host: use uint16_t for Language ID

usbh_req_desc() truncates the descriptor id. This problem is most
visible with string descriptor requests, as only then can wIndex be
greater than 0xFF. In particular, this affects commonly used language
IDs such as English (United States), which is 0x0409.

Signed-off-by: Alexander Kaiser <akaiser@urbansky.com>