slub: make struct kmem_cache_order_objects::x unsigned int

struct kmem_cache_order_objects is for mixing order and number of
objects, and orders aren't big enough to warrant 64-bit width.

Propagate unsignedness down so that everything fits.

!!! Patch assumes that "PAGE_SIZE << order" doesn't overflow. !!!

Link: http://lkml.kernel.org/r/20180305200730.15812-23-adobriyan@gmail.com
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: 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>