xhci: remove unused lpm_failed_dev member from struct xhci_hcd

xhci used to test if link power management (LPM) capable USB2 devices
really could enter and exit L1 state link state.
Failed devices were added to a lpm_failed_dev list.

This feature was removed 9 years ago in
commit de68bab4

 ("usb: Don't enable USB 2.0 Link PM by default.")
but lpm_failed_dev member was still left.

Remove it now.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220921123450.671459-7-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>