Fix the array size of mpidr_aff_map_nodes_t.

This patch fixes the array size of mpidr_aff_map_nodes_t which
was less by one element.

Fixes ARM-software/tf-issues#264

Change-Id: I48264f6f9e7046a3d0f4cbcd63b9ba49657e8818
Merge pull request #224 from soby-mathew/sm/fix_mpidr_aff_map_nodes_t

Fix the array size of mpidr_aff_map_nodes_t.