Started a Cocos2D 2.1 template (with no physics engine) in Xcode 4.5, targeted for iOS 6 and iPad. In the CDAudioManager.m file, the following code...
AVAudioSe
The error you are running into is in this block of code
AVAudioSession* session = [AVAudioSession sharedInstance];
session.delegate = self;// <-------- DEPRECATED IN IOS 6.0
To silence the warning change those 2 lines to this:
[[AVAudioSession sharedInstance] setActive:YES error:nil];
Hope this helps.