x86: cacheinfo: disable L3 ECC scrubbing when L3 cache index is disabled

(Use correct mask to zero out bits 24-28 by Andreas)

Signed-off-by: Mark Langsdorf <mark.langsdorf@amd.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <20090409132406.GK31527@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>