usb: gadget: udc-core: prevent a memory leak

udc-core would leak 'udc' memory in some error
cases. Fix it by kfree()ing udc on error path.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc-core.c

@@ -240,6 +240,7 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 
 err2:
 	put_device(&gadget->dev);
+	kfree(udc);
 
 err1:
 	return ret;