USB: ohci: set urb->hcpriv = NULL immediately, after free it

although we can not say it is surely a bug.
it is better to set urb->hcpriv = NULL, after finish calling
urb_free_priv.

Signed-off-by: Chen Gang <[e-mail]>
Acked-by: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/ohci-q.c

···
 	// ASSERT (urb->hcpriv != 0);
 
 	urb_free_priv (ohci, urb->hcpriv);
+	urb->hcpriv = NULL;
 	if (likely(status == -EINPROGRESS))
 		status = 0;