slab: fix to calm down kmemleak warning

After using struct page as slab management, we should not call
kmemleak_scan_area(), since struct page isn't the tracking object of
kmemleak. Without this patch and if CONFIG_DEBUG_KMEMLEAK is enabled,
so many kmemleak warnings are printed.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Pekka Enberg <penberg@iki.fi>
slab: replace non-existing 'struct freelist *' with 'void *'

There is no 'strcut freelist', but codes use pointer to 'struct freelist'.
Although compiler doesn't complain anything about this wrong usage and
codes work fine, but fixing it is better.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Pekka Enberg <penberg@iki.fi>
Merge branch 'slab/struct-page' into for-next