Don't directly cast list_head * to foo *, this works only when list
is the first member of struct foo, and we should not make the assumption
how members are ordered in the structure.

i.e. struct *f = (struct *f)pos will work if:
	struct foo {
		struct list_head list;
		int i;
	};

but will fail if:
	struct foo {
		int i;
		struct list_head list;
	}
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>