usb: gadget: Fix controller index in UMS

The usb mass storage (f_mass_storage.c) uses fixed usb index 0,
this causes problem while CDNS3 USB controller index is 1.
Modify the API of fsg to pass the controller index.

Reviewed-by: Jun Li <jun.li@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>