[OpenCL] Possible waist of resources in silx

[kif]

RepeatedKernelRetrieval: Kernel 'decimate' has been retrieved more than once. Each retrieval creates a new, independent kernel, at possibly considerable expense. To avoid the expense, reuse the retrieved kernel instance. To avoid this warning, use cl.Kernel(prg, name).
  prg.decimate(q, (width_out, height_out), None,