EDAC, sb_edac: Drop NUM_CHANNELS from 8 back to 4

We don't need this quirk anymore now that the EDAC memory controller
representation matches the hardware.

Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170523000834.87881-1-qiuxu.zhuo@intel.com
[ Commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>