slub: Fix debugobjects with lockless fastpath

On Thu, 24 Mar 2011, Ingo Molnar wrote:
> RIP: 0010:[<ffffffff810570a9>]  [<ffffffff810570a9>] get_next_timer_interrupt+0x119/0x260

That's a typical timer crash, but you were unable to debug it with
debugobjects because commit d3f661d6 broke those.

Cc: Christoph Lameter <cl@linux.com>
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Pekka Enberg <penberg@kernel.org>