Update one remaining & to pending_receiver

This one part somehow escaped getting upgraded to the new Mojo names.

Bug: None
Test: Build
Change-Id: Icb4cc5a4c65429a026866e847288a92d0542dc69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015900
Commit-Queue: Andrew Moylan <amoylan@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Auto-Submit: Andrew Moylan <amoylan@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734222}

chromeos/services/machine_learning/public/mojom/machine_learning_service.mojom

@@ -29,10 +29,11 @@ enum LoadModelResult {
 interface MachineLearningService {
   // The BuiltinModelId inside BuiltinModelSpec is used to specify the model to
   // be loaded.
-  LoadBuiltinModel(BuiltinModelSpec spec, Model& request)
+  LoadBuiltinModel(BuiltinModelSpec spec, pending_receiver<Model> receiver)
       => (LoadModelResult result);
   // The FlatbufferModelSpec contains both of the flatbuffer content and the
   // metadata.
-  LoadFlatBufferModel(FlatBufferModelSpec spec, Model& request)
+  LoadFlatBufferModel(FlatBufferModelSpec spec,
+                      pending_receiver<Model> receiver)
       => (LoadModelResult result);
 };