This isn't a real bug as the smallest slab-size is 32 bytes but please
apply for consistency.

Found by the Coverity tool.
Signed-off-by: Alexander Nyberg <alexn@dsv.su.se>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>