BaseTools: Fix Sku inherit issue.

The final Pcd value should only be override by its parents.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Feng Bob C <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/Python/Common/Misc.py

@@ -2251,6 +2251,8 @@ class SkuClass():
         return self.__SkuInherit.get(skuname,"DEFAULT")
 
     def GetSkuChain(self,sku):
+        if sku == "DEFAULT":
+            return ["DEFAULT"]
         skulist = [sku]
         nextsku = sku
         while 1: