usb: dwc2: host: Setting qtd to NULL after freeing it

This is safety change added while doing slub debugging.

Affected functions:
dwc2_hcd_qtd_unlink_and_free()
_dwc2_hcd_urb_enqueue()
Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc2/hcd.c

@@ -4703,6 +4703,7 @@ static int _dwc2_hcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
 	spin_unlock_irqrestore(&hsotg->lock, flags);
 	urb->hcpriv = NULL;
 	kfree(qtd);
+	qtd = NULL;
 fail1:
 	if (qh_allocated) {
 		struct dwc2_qtd *qtd2, *qtd2_tmp;

drivers/usb/dwc2/hcd.h

@@ -552,6 +552,7 @@ static inline void dwc2_hcd_qtd_unlink_and_free(struct dwc2_hsotg *hsotg,
 {
 	list_del(&qtd->qtd_list_entry);
 	kfree(qtd);
+	qtd = NULL;
 }
 
 /* Descriptor DMA support functions */