usb: don't use flush_scheduled_work()

flush_scheduled_work() is being deprecated.  Directly flush or cancel
work items instead.

* u_ether, isp1301_omap, speedtch conversions are straight-forward.

* ochi-hcd should only flush when quirk_nec() is true as otherwise the
  work wouldn't have been initialized.

* In oti6858, cancel_delayed_work() + flush_scheduled_work() ->
  cancel_delayed_work_sync().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Duncan Sands <duncan.sands@free.fr>
Cc: linux-usb@vger.kernel.org