The cpu_2_node array for i386 is initialized to 0 for each CPU, 
effectively mapping all CPUs to node 0 unless changed.  When we unmap 
CPUs, however, we stick a -1 in the array, mapping the CPU to an invalid 
node.  This really isn't helpful.  We should map the CPU to node 0, to 
make sure that callers of cpu_to_node() and friends aren't returned a 
bogus node number.  This trivial patch changes the unmapping code to 
place a 0 in the node mapping for removed CPUs.

Cheers!

-Matt