slub: make ->max_attr_size unsigned int

->max_attr_size is maximum length of every SLAB memcg attribute
ever written. VFS limits those to INT_MAX.

Link: http://lkml.kernel.org/r/20180305200730.15812-10-adobriyan@gmail.com
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.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>