jz4740_udc.c: tentative fix for upstream changes in USB driver framework

This specifically addresses this sort of changes:

fc84d2fbe776f5352c3a981a5250a3ad83789f72  let udc-core manage gadget->dev
7bce401cc6db5508ef2517e45bd8caf7ce0a15ee  drop now unnecessary flag

"... because all UDC drivers have been properly converted." (which of
course doesn't apply to our out-of-tree driver)