EDAC: Fix mc size reported in sysfs

This is the complement to previous commit "EDAC: Fix csrow size
reported in sysfs". This fixes the memory controller size reporting on
csrow-based memory controllers. The csrow size is already combined for
both channels. Without this patch memory size is reported doubled.

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