mm/slab: rerform init_on_free earlier

Currently in CONFIG_SLAB init_on_free happens too late, and heap objects
go to the heap quarantine not being erased.

Lets move init_on_free clearing before calling kasan_slab_free().  In that
case heap quarantine will store erased objects, similarly to CONFIG_SLUB=y
behavior.

Link: https://lkml.kernel.org/r/20201210183729.1261524-1-alex.popov@linux.com
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>