USB: gadget: atmel: disconnect before unbind

When unbind the gadget driver, need call disconnect first.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
diff --git a/drivers/usb/gadget/atmel_usba_udc.c b/drivers/usb/gadget/atmel_usba_udc.c
index f146c48..c99208d 100644
--- a/drivers/usb/gadget/atmel_usba_udc.c
+++ b/drivers/usb/gadget/atmel_usba_udc.c
@@ -1240,11 +1240,12 @@
 {
 	struct usba_udc *udc = &controller;
 
-	if (!driver || !driver->bind || !driver->setup) {
+	if (!driver || !driver->unbind || !driver->disconnect) {
 		error("bad paramter\n");
 		return -EINVAL;
 	}
 
+	driver->disconnect(&udc->gadget);
 	driver->unbind(&udc->gadget);
 	udc->driver = NULL;