tools/vm/slabinfo: cosmetic globals cleanup

checkpatch.pl complains about globals being explicitly zeroed
out: "ERROR: do not initialise globals to 0 or NULL".

New globals, introduced in this patch set, have no explicit 0
initialization; clean up the old ones to make it less hairy.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>