edac: use to_delayed_work()

The edac-core driver includes code which assumes that the work_struct
which is included in every delayed_work is the first member of that
structure.  This is currently the case but might change in the future, so
use to_delayed_work() instead, which doesn't make such an assumption.

linux-2.6.30-rc1 has the to_delayed_work() function that will allow this
patch to work

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>