usb: gadget: ci_udc: implement usb_ep_ops dequeue callback

usb: gadget: ci_udc: implement usb_ep_ops dequeue callback

Implement endpoint dequeue callback function.

Without this function, uboot will hang when executing fastboot comamnd.
See following flow:
"fastboot_tx_write_str->fastboot_tx_write->usb_ep_dequeue->ep->ops->dequeue"
without implement ci_udc dequeue function, ep->ops->dequeue is NULL, then
uboot will hang.

Tested on mx6qsabresd board with fastboot enabled.

Signed-off-by: Peng Fan <[email protected]>
Tested-by: Fabio Estevam <[email protected]>
Cc: "Łukasz Majewski" <[email protected]>
Cc: Marek Vasut <[email protected]>