Fixes a return type mismatch in suggestions service factory.

ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc

Index: ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
diff --git a/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc b/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
index e04514422512665dc83de433afab4325fa7124d5..151b5d47b195da9564b086f11c4c442d135a09c5 100644
--- a/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
+++ b/ios/chrome/browser/ntp_snippets/ios_chrome_content_suggestions_service_factory.cc
@@ -120,7 +120,7 @@ IOSChromeContentSuggestionsServiceFactory::BuildServiceInstanceFor(
   std::unique_ptr<ContentSuggestionsService> service =
       base::MakeUnique<ContentSuggestionsService>(state);
   if (state == State::DISABLED)
-    return service;
+    return std::move(service);
 
   // Create the BookmarkSuggestionsProvider.
   if (base::FeatureList::IsEnabled(ntp_snippets::kBookmarkSuggestionsFeature)) {
@@ -171,5 +171,5 @@ IOSChromeContentSuggestionsServiceFactory::BuildServiceInstanceFor(
     service->RegisterProvider(std::move(ntp_snippets_service));
   }
 
-  return service;
+  return std::move(service);
 }