edac: store/show methods for device groups weren't working

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

diff --cc drivers/edac/edac_core.h
Simple merge

diff --cc drivers/edac/edac_mc_sysfs.c
Simple merge

diff --cc drivers/edac/i7core_edac.c
Simple merge