mm: kasan: remove unused 'reserved' field from struct kasan_alloc_meta

mm: kasan: remove unused 'reserved' field from struct kasan_alloc_meta

Commit cf74bee464ab ("mm, kasan: stackdepot implementation.  Enable
stackdepot for SLAB") added 'reserved' field, but never used it.

Link: http://lkml.kernel.org/r/1464021054-2307-1-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>