IntelSiliconPkg IntelVTdDxe: Signal AcpiNotificationFunc() initially

Signal AcpiNotificationFunc() initially for the case that
DMAR table has been installed when creating event.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
(cherry picked from commit dcd39e09ff)

IntelSiliconPkg/Feature/VTd/IntelVTdDxe/DmarAcpiTable.c

@@ -1005,6 +1005,9 @@ GetDmarAcpiTable (
                &AcpiTable
                );
   }
+  if (EFI_ERROR (Status)) {
+    return EFI_NOT_FOUND;
+  }
   ASSERT (AcpiTable != NULL);
 
   mAcpiDmarTable = FindAcpiPtr (