Only check for CL errors at end of parent filter functions.
Only check for CL errors at end of parent filter functions.

The 1st/second pass won't corrupt any data if they fail, so we can get away
with checking only once at the end.

awatry/libvpx.opencl,awatry/libvpx.opencl,awatry/libvpx.opencl,awatry/libvpx.opencl