i7core_edac: Check probe counter in i7core_remove

Prevent i7core_remove from running multiple times.
Otherwise value proved will be negative and something will be wrong.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>