amd64_edac: Fix K8 chip select reporting

This basically reverts 603adaf6 ("amd64_edac: fix K8 chip select
reporting") because it was a clumsy workaround for DIMM sizes reporting
on K8 which got superceded by a much more correct one with 41d8bfab


("amd64_edac: Improve DRAM address mapping") without removing the prior
one. Remove it now finally.

Reported-by: Josh Hunt <johunt@akamai.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>