usb: xhci: Free the right ring in xhci_add_endpoint()
In the xhci_add_endpoint(), a new ring was allocated and saved at
xhci_virt_ep->new_ring. Hence, when error happens, we need to free
the allocated ring before returning error.
Current code frees xhci_virt_ep->ring instead of the new_ring. This
patch fixes this.