slub: Disable interrupts in free_debug processing

We will be calling free_debug_processing with interrupts disabled
in some case when the later patches are applied. Some of the
functions called by free_debug_processing expect interrupts to be
off.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>