slub: Check kasprintf results in kmem_cache_init()

Small allocations may fail during slab bringup which is fatal. Add a BUG_ON()
so that we fail immediately rather than failing later during sysfs
processing.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>