AudioDevices HAL uses "default" service name

The getService() and registerAsService() methods of interface objects
now have default parameters of "default" for the service name. HALs
will not have to use any service name unless they want to register
more than one service.

Test: builds

Bug: 33844934
Change-Id: Ifc6d297d0bbf7b28be560700c027c07acaa2466c
diff --git a/media/libaudiohal/DevicesFactoryHalHidl.cpp b/media/libaudiohal/DevicesFactoryHalHidl.cpp
index b0f28b9..9cbe018 100644
--- a/media/libaudiohal/DevicesFactoryHalHidl.cpp
+++ b/media/libaudiohal/DevicesFactoryHalHidl.cpp
@@ -40,7 +40,7 @@
 }
 
 DevicesFactoryHalHidl::DevicesFactoryHalHidl() {
-    mDevicesFactory = IDevicesFactory::getService("audio_devices_factory");
+    mDevicesFactory = IDevicesFactory::getService();
     if (mDevicesFactory != 0) {
         // It is assumet that DevicesFactory is owned by AudioFlinger
         // and thus have the same lifespan.