What type of failure? Doesn't print anything or prints wrong result? Or some other error?
Currently, I don't think cl_amd_printf extension is required any more. It was introduced for earlier drivers.
AFAIK, printf works fine with latest driver and APP SDK. However, as I checked some time ago, there was an issue particularly for OpenCL 2.0 kernel build. If your issue still persists, please provide the test code and mention your setup details.