AdvancedFeaturePkg/BmcElog: Change arithmetic logic

Change the value from "sizeof(UINT8)" to 1 in the arithmetic expression.
The original value added to (UINT8 *)&GetBmcGlobalEnables is
(sizeof(UINT8)*sizeof(UINT8)) which equals to 1, so the functionality
looks right. But the arithmetic logic is actually wrong.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>