EDAC, sb_edac: Fix out of bound writes during DIMM configuration on KNL

Commit

  3286d3eb

 ("EDAC, sb_edac: Drop NUM_CHANNELS from 8 back to 4")

decreased NUM_CHANNELS from 8 to 4, but this is not enough for Knights
Landing which supports up to 6 channels.

This caused out-of-bounds writes to pvt->mirror_mode and pvt->tolm
variables which don't pay critical role on KNL code path, so the memory
corruption wasn't causing any visible driver failures.

The easiest way of fixing it is to change NUM_CHANNELS to 6. Do that.

An alternative solution would be to restructure the KNL part of the
driver to 2MC/3channel representation.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Anna Karbownik <anna.karbownik@intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: jim.m.snow@intel.com
Cc: krzysztof.paliswiat@intel.com
Cc: lukasz.odzioba@intel.com
Cc: qiuxu.zhuo@intel.com
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Fixes: 3286d3eb

 ("EDAC, sb_edac: Drop NUM_CHANNELS from 8 back to 4")
Link: http://lkml.kernel.org/r/1519312693-4789-1-git-send-email-anna.karbownik@intel.com
[ Massage commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>