GPU Calc: revert back to OpenCL fmin and fmax

When generating code for MIN and MAX an integer version (min/max) isn't
correct.

Change-Id: I4bf1e774e37e0ce30924178f022156e0e43f4c06
GPU Calc: fix compilation error in using sprintf

Change-Id: Iea316f3355a9105702391aa7b76268cdfc8831ef