Add an argument to the workgroup-size-query kernel

On OSX, the OpenCL compiler doesn't like a kernel that takes no
arguments. This causes an exception to be raised, and eventually
crashes the application. By adding an argument, we allow the kernel to
be compiled

This fixes #7
Merge pull request #19 from branan/osx_fixes

Add an argument to the workgroup-size-query kernel

Alright, I can verify that this did not introduce a regression on the linux code. Merging, and thanks for the patch!