EDAC: Correct MiB_TO_PAGES() macro

This corrects the misprint introduced when moving '#if
PAGE_SHIFT' from i7core_edac.c to edac_core.h (commit
e9144601)

Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Andrei Konovalov <akonovalov@mvista.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>