Add clWaitForEvents first

Before: 
> run/john -format=encfs-opencl -te 
Will run 4 OpenMP threads
Device 0: Intel(R) HD Graphics IvyBridge M GT2
OpenCL error (CL_PROFILING_INFO_NOT_AVAILABLE) in file (common-opencl.c) at line (1210) - (Failed in clGetEventProfilingInfo I)

Now:
> run/john -format=encfs-opencl -te
Will run 4 OpenMP threads
Device 0: Intel(R) HD Graphics IvyBridge M GT2
Local worksize (LWS) 64, global worksize (GWS) 64
Benchmarking: encfs-opencl, EncFS [PBKDF2-SHA1 OpenCL 4x AES/Blowfish]... (4xOMP) DONE
Raw:	7.8 c/s real, 4266 c/s virtual