usb-xhci: ready the link trb early
usb-xhci: ready the link trb early

The keyboard events being async, need to prepare the link when last but
one trb is queued.

Signed-off-by: Nikunj A Dadhania <e2f4a5db9b4735182a88051d1e7a3599f9eac9db@linux.vnet.ibm.com>

open-power-host-os/slof,open-power-host-os/slof,open-power-host-os/slof,open-power-host-os/slof