Fix up SLUB compile

The newly merged SLUB allocator patches had been generated before the
removal of "struct subsystem", and ended up applying fine, but wouldn't
build based on the current tree as a result.

Fix up that merge error - not that SLUB is likely really ready for
showtime yet, but at least I can fix the trivial stuff.

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