amd64_edac: fix use-uninitialised bug

drivers/edac/amd64_edac.c: In function 'amd64_edac_init':
drivers/edac/amd64_edac.c:2840: warning: 'ret' may be used uninitialized in this function

Cc: Doug Thompson <dougthompson@xmission.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>