Fix "warning: cast from pointer to integer of different size"

[Dmitry Timoshkov]

"Erik de Castro Lopo" <mle+win at mega-nerd.com> wrote:

> /* get pointer to object containing list element */
> #define LIST_ENTRY(elem, type, field) \
> -    ((type *)((char *)(elem) - (unsigned int)(&((type *)0)->field)))
> +    ((type *)((char *)(elem) - (unsigned long)(&((type *)0)->field)))

It should be replaced with FIELD_OFFSET instead.

-- 
Dmitry.