arch_topology: Check for non-negative value rather than -1 for IDs validity

Instead of just comparing the cpu topology IDs with -1 to check their
validity, improve that by checking for a valid non-negative value.

Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>