slab: use 32-bit arithmetic in freelist_randomize()

slab: use 32-bit arithmetic in freelist_randomize()

SLAB doesn't support 4GB+ of objects per slab, therefore randomization
doesn't need size_t.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexey Dobriyan <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>