usb: dwc3: ep0: only change to ADDRESS if set_config() succeeds

In case we're switching back to USB_STATE_ADDRESS
from USB_STATE_CONFIGURED (if host sends
a set configuration command for configuration
zero), we should only switch if the request
is successfully processed by the gadget driver.

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>