speedtch: don't abuse struct delayed_work

speedtch directly uses the internal timer and work members of a struct
delayed_work.  Use a separate work item and timer instead.

* Nicolas Kaiser discovered that timer init was missing.  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Tested-by: Nicolas Kaiser <nikai@nikai.net>
Cc: Duncan Sands <duncan.sands@free.fr>
Cc: linux-usb@vger.kernel.org