mfd: update workqueue usages

mfd: update workqueue usages

flush_scheduled_work() is deprecated and scheduled to be removed.

* In menelaus, flush menelaus->work directly on probe failure.  Also,
  make sure the work isn't running on removal.

* In tps65010, cancel_delayed_work() + flush_scheduled_work() ->
  cancel_delayed_work_sync().  While at it, remove unnecessary (void)
  casts on return value, and use schedule_delayed_work() and
  to_delayed_work() instead of using delayed_work's internal work
  field.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Samuel Ortiz <sameo@linux.intel.com>