buffet: fix -Winconsistent-missing-override warning.

BUG=chromium:453077
TEST=FEATURES="test" emerge-amd64-generic buffet

Change-Id: Ibf5587a47a8dbe5d83f313b88576826cbeae3005
Reviewed-on: https://chromium-review.googlesource.com/244060
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>

buffet/commands/prop_constraints.h

diff --git a/buffet/commands/prop_constraints.h b/buffet/commands/prop_constraints.h
index 4054f30..ae93ccf 100644
--- a/buffet/commands/prop_constraints.h
+++ b/buffet/commands/prop_constraints.h
@@ -130,7 +130,7 @@
       : ConstraintMinMaxBase<T>(limit) {}
 
   // Implementation of Constraint::GetType().
-  ConstraintType GetType() const { return ConstraintType::Min; }
+  ConstraintType GetType() const override { return ConstraintType::Min; }
 
   // Implementation of Constraint::Validate().
   bool Validate(const PropValue& value,
@@ -167,7 +167,7 @@
       : ConstraintMinMaxBase<T>(limit) {}
 
   // Implementation of Constraint::GetType().
-  ConstraintType GetType() const { return ConstraintType::Max; }
+  ConstraintType GetType() const override { return ConstraintType::Max; }
 
   // Implementation of Constraint::Validate().
   bool Validate(const PropValue& value,