usb: xhci: remove duplicate function xhci_urb_to_transfer_ring

Remove duplicate function xhci_urb_to_transfer_ring from xhci.c.
We have same function in xhci-ring.c.

Signed-off-by: Alexandr Ivanov <alexandr.sky@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>