i7core_edac: change remove module strategy

The old remove module stragegy didn't work on devices with multiple
cores, since only one PCI device is used to open all mc's, due to
Nehalem nature.

Also, it were based at pdev value. However, this doesn't point to the
pci device used at mci->dev.

So, instead, it unregisters all devices at once, deleting them from the
device list.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>