staging: r8188eu: remove the _cancel_workitem_sync wrapper

Remove the _cancel_workitem_sync wrapper and call
cancel_work_sync directly.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211125162513.25039-4-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>