usb: gadget: goku_udc: avoid NULL deref of dev->driver in INT_USBRESET log

usb: gadget: goku_udc: avoid NULL deref of dev->driver in INT_USBRESET log

goku_irq() handles a number of bus events under a single ep0 path.
It already guards the gadget driver suspend/resume callbacks against a
NULL ->driver:

	if (dev->gadget.speed != USB_SPEED_UNKNOWN
			&& dev->driver
			&& dev->driver->resume) {
		spin_unlock(&dev->lock);
		dev->driver->resume(&dev->gadget);
		...
	}

but the very next branch unconditionally dereferences dev->driver
when an INT_USBRESET arrives:

	if (stat & INT_USBRESET) {
		ACK(INT_USBRESET);
		INFO(dev, "USB reset done, gadget %s\n",
			dev->driver->driver.name);
	}

If the controller raises INT_USBRESET before any gadget driver has
been bound (or after one has been unbound), dev->driver is NULL and
the printk dereferences NULL.

smatch flags the inconsistency:

  drivers/usb/gadget/udc/goku_udc.c:1618 goku_irq() error:
  we previously assumed 'dev->driver' could be null (see line 1607)

Fall back to a placeholder when the gadget driver is not bound.

No functional change while a gadget driver is bound.

Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
Link: https://patch.msgid.link/20260509110636.19762-1-sozdayvek@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>