MdeModulePkg/PciHostBridgeDxe: Fix VS tool chain build failure

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Shumin Qiu <shumin.qiu@intel.com>

MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciRootBridgeIo.c

@@ -199,6 +199,7 @@ CreateRootBridge (
       break;
     default:
       ASSERT (FALSE);
+      Aperture = NULL;
       break;
     }
     RootBridge->ResAllocNode[Index].Type     = Index;