i7core_edac: Avoid doing multiple probes for the same card

As Nehalem/Nehalem-EP/Westmere devices uses several devices for the same
functionality (memory controller), the default way of proping devices doesn't
work. So, instead of a per-device probe, all devices should be probed at once.

This means that we should block any new attempt of probe, otherwise, it will
try to register the same device several times.

Acked-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>