zone_pcp() only returns valid values if the processor is online.

Change node_read_numastat() to only scan online processors.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>