EDAC/ie31200: Fix the DIMM size mask for several SoCs

The DIMM size mask for {Sky, Kaby, Coffee} Lake is not bits{7:0},
but bits{5:0}. Fix it.

Fixes: 953dee9b ("EDAC, ie31200_edac: Add Skylake support")
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Tested-by: Gary Wang <gary.c.wang@intel.com>
Link: https://lore.kernel.org/r/20250310011411.31685-3-qiuxu.zhuo@intel.com