kasan: only select SLUB_DEBUG with SYSFS=y

kasan: only select SLUB_DEBUG with SYSFS=y

Building with KASAN and SLUB but without sysfs now results in a
build-time error:

  WARNING: unmet direct dependencies detected for SLUB_DEBUG
    Depends on [n]: SLUB [=y] && SYSFS [=n]
    Selected by [y]:
    - KASAN [=y] && HAVE_ARCH_KASAN [=y] && (SLUB [=y] || SLAB [=n] && !DEBUG_SLAB [=n]) && SLUB [=y]
  mm/slub.c:4565:12: error: 'list_locations' defined but not used [-Werror=unused-function]
   static int list_locations(struct kmem_cache *s, char *buf,
              ^~~~~~~~~~~~~~
  mm/slub.c:4406:13: error: 'validate_slab_cache' defined but not used [-Werror=unused-function]
   static long validate_slab_cache(struct kmem_cache *s)

This disallows that broken configuration in Kconfig.

Link: http://lkml.kernel.org/r/20180709154019.1693026-1-arnd@arndb.de
Fixes: dd275caf4a0d ("kasan: depend on CONFIG_SLUB_DEBUG")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>