The 64-core versions of the Ampere Altra SoC still have 80 redistributors.

The 64-core versions of the Ampere Altra SoC still have 80 redistributors.
Presumably these are the same silicon and the 64-core version just has some
of the cores disabled.  This means that the redistributors don't necessarily
all match up with a core that is actually enabled.  So remove the panic
that would happen if we found a redistributor without a matching core.

ok patrick@, deraadt@