mm/slub: correct the comment in calculate_order()

mm/slub: correct the comment in calculate_order()

In calculate_order(), it tries to calculate the best order by adjusting
the fraction and min_objects.  On each iteration on min_objects, fraction
iterates on 16, 8, 4.  Which means the acceptable waste increases with
1/16, 1/8, 1/4.

This patch corrects the comment according to the code.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>