i7core_edac: fix error injection

There were two stupid error injection bugs introduced by wrong
cut-and-paste: one at socket store, and another at the error inject
register. The last one were causing the code to not work at all.

While here, adds debug messages to allow seeing what registers are being
set while sending error injection.

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