x86-64, NUMA: Fix size of numa_distance array

numa_distance should be sized like the SLIT, an NxN matrix where N is
the highest node id + 1.  This patch fixes the calculation to avoid
overflowing the array on the subsequent iteration.

-tj: The original patch used last index to calculate size.  Yinghai
     pointed out it should be incremented so it is the number of
     elements instead of the last index to calculate the size of the
     table.  Updated accordingly.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>