i7core_edac: fixed typo in error count calculation

Based on a patch from the PaX Team, found during a clang analysis pass.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: PaX Team <pageexec@freemail.hu>
Cc: stable@kernel.org [v2.6.35+]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>