xhci: Fix xhci debugfs devices node disappearance after hibernation
During system resume from hibernation, xhci host is reset, all the
nodes in devices folder are removed in xhci_mem_cleanup function.
Later nodes in /sys/kernel/debug/usb/xhci/* are created again in
function xhci_run, but the nodes already exist, so the nodes still
keep the old ones, finally device nodes in xhci debugfs folder
/sys/kernel/debug/usb/xhci/*/devices/* are disappeared.
This fix removed xhci debugfs nodes before the nodes are re-created,
so all the nodes in xhci debugfs can be re-created successfully.