NUMA: Replace MAX_NODES with nb_numa_nodes in for loop

NUMA: Replace MAX_NODES with nb_numa_nodes in for loop

In QEMU, the number of the NUMA nodes is determined by parse_numa_opts().
Then, QEMU uses it for iteration, for example:
  for (i = 0; i < nb_numa_nodes; i++)

However, in memory_region_allocate_system_memory(), it uses MAX_NODES
not nb_numa_nodes.

So, replace MAX_NODES with nb_numa_nodes to keep code consistency and
reduce the loop times.

Signed-off-by: Dou Liyang <[email protected]>
Message-Id: <1503387936[email protected]>
Reviewed-by: Igor Mammedov <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>