xhci: turn cancelled td cleanup to its own function

Refactor handler for stop endpoint command completion. Yank out the part
that invalidates cancelled TDs and turn it into a separate function.

Invalidating cancelled TDs should be done while the ring is stopped,
but not exclusively in the stop endpoint command completeion handler.

We will need to invalidate TDs after resetting endpoints as well.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210129130044.206855-20-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>