Stub implementation for USB audio HAL.

Bug: 266216550
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Ida4b3dbdb684dfc880a907651ae0fc398addbffc
diff --git a/audio/aidl/default/main.cpp b/audio/aidl/default/main.cpp
index b66c134..1933509 100644
--- a/audio/aidl/default/main.cpp
+++ b/audio/aidl/default/main.cpp
@@ -55,7 +55,8 @@
         return std::make_pair(module, moduleBinder);
     };
     auto modules = {createModule(Module::Type::DEFAULT, "default"),
-                    createModule(Module::Type::R_SUBMIX, "r_submix")};
+                    createModule(Module::Type::R_SUBMIX, "r_submix"),
+                    createModule(Module::Type::USB, "usb")};
 
     ABinderProcess_joinThreadPool();
     return EXIT_FAILURE;  // should not reach