EDAC, sb_edac: Remove variable length array usage

In preparation for enabling -Wvla, remove VLA and replace it with a
fixed-length array instead.

Also, remove max_interleave as it is no longer needed.

Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20180314182131.GA25259@embeddedgus
Signed-off-by: Borislav Petkov <bp@suse.de>