mm/kasan: use SLAB_NO_MERGE flag instead of an empty constructor

mm/kasan: use SLAB_NO_MERGE flag instead of an empty constructor

Use SLAB_NO_MERGE flag to prevent merging instead of providing an empty
constructor.  Using an empty constructor in this manner is an abuse of
slab interface.

The SLAB_NO_MERGE flag should be used with caution, but in this case, it
is acceptable as the cache is intended solely for debugging purposes.

No functional changes intended.

Link: https://lkml.kernel.org/r/20250318015926.1629748-1-harry.yoo@oracle.com
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Acked-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>