Fix "check_slabp" printout size calculation

We want to use the "struct slab" size, not the size of the pointer to
same.  As it is, we'd not print out the last <n> entry pointers in the
slab (where <n> is ~10, depending on whether it's a 32-bit or 64-bit
kernel).

Gaah, that slab code was written by somebody who likes unreadable crud.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>