usb: gadget: fix a bug and a WARN_ON in dummy-hcd

This patch fixes a NULL pointer dereference and a WARN_ON in
dummy-hcd.  These things were the result of moving to the UDC core
framework, and possibly of changes to that framework.

Now unloading a gadget driver causes the UDC to be stopped after the
gadget driver is unbound, not before.  Therefore the "driver" argument
to dummy_udc_stop() can be NULL, so we must not try to print the
driver's name without checking first.

Also, the UDC framework automatically unregisters the gadget when the
UDC is deleted.  Therefore a sysfs attribute file attached to the
gadget must be removed before the UDC is deleted, not after.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/gadget/dummy_hcd.c

@@ -923,8 +923,9 @@ static int dummy_udc_stop(struct usb_gadget *g,
 	struct dummy_hcd	*dum_hcd = gadget_to_dummy_hcd(g);
 	struct dummy		*dum = dum_hcd->dum;
 
-	dev_dbg(udc_dev(dum), "unregister gadget driver '%s'\n",
-			driver->driver.name);
+	if (driver)
+		dev_dbg(udc_dev(dum), "unregister gadget driver '%s'\n",
+				driver->driver.name);
 
 	dum->driver = NULL;
 
@@ -1000,8 +1001,8 @@ static int dummy_udc_remove(struct platform_device *pdev)
 {
 	struct dummy	*dum = platform_get_drvdata(pdev);
 
-	usb_del_gadget_udc(&dum->gadget);
 	device_remove_file(&dum->gadget.dev, &dev_attr_function);
+	usb_del_gadget_udc(&dum->gadget);
 	return 0;
 }