usb: gadget: udc: Potential Oops in error handling code

If this is in "transceiver" mode the the ->qwork isn't required and is
a NULL pointer.  This can lead to a NULL dereference when we call
destroy_workqueue(udc->qwork).

Fixes: 3517c31a ("usb: gadget: mv_udc: use devm_xxx for probe")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/udc/mv_udc_core.c

@@ -2313,6 +2313,7 @@ static int mv_udc_probe(struct platform_device *pdev)
 	return 0;
 
 err_create_workqueue:
+	if (udc->qwork)
 		destroy_workqueue(udc->qwork);
 err_destroy_dma:
 	dma_pool_destroy(udc->dtd_pool);