EDAC/ie31200: Fold the two channel loops into one loop

Fold the two channel loops to simplify the code and improve readability.
Also, delete the comments related to the DRB register, as this register
is not used here.

 No functional changes intended.

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/20250310011411.31685-9-qiuxu.zhuo@intel.com