amd64_edac: Correct DIMM sizes

We were filling the csrow size with a wrong value. 16a528ee3975 ("EDAC:
Fix csrow size reported in sysfs") tried to address the issue. It fixed
the report with the old API but not with the new one. Correct it for the
new API too.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
[ make it a per-csrow accounting regardless of ->channel_count ]
Signed-off-by: Borislav Petkov <bp@suse.de>