libertas: don't cast a pointer to pointer of

Don't cast struct foo * to struct list_head *, it's safe only when
the list member is the first member of struct foo.

Also don't cast struct list_head * to struct foo *.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>