Bluetooth: btusb: fix bInterval for high/super speed isochronous endpoints

For high-speed/super-speed isochronous endpoints, the bInterval
value is used as exponent, 2^(bInterval-1). Luckily we have
usb_fill_int_urb() function that handles it correctly. So we just
call this function to fill in the RX URB.

Cc: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>