amd64_edac: fix K8 chip select reporting

Fix the case when amd64_debug_display_dimm_sizes() reports only half the
amount of DRAM on it because it doesn't account for when the single DCT
operates in 128-bit mode and merges chip selects from different DIMMs.

Reported-by: Johannes Hirte <johannes.hirte@fem.tu-ilmenau.de>
LKML-Reference: <200912112202.48173.johannes.hirte@fem.tu-ilmenau.de>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>