amd64_edac: fix interleave enable tests

The pvt->dram_IntlvEn saves the 3 "Interleave Enable" bits already
right-shifted by 8 so the check in find_mc_by_sys_addr() by shifting the
values to the left 8 bits is wrong.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>