MAINTAINERS: SLAB maintainer update

As discussed in various threads on the side:

Remove one inactive maintainer, add two new ones and update my email
address.  Plus add Andrew.  And fix the glob to include files like
mm/slab_common.c

Signed-off-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>