You can't directly collect entropy from OpenCL's device memory. That requires some *SSL call followed by a copy-from-host-to-device call.
I got curious and did quick google search. I found presentation file which state there are 5 OpenCL RNG library/implementation (Random123, MTGP, OpenCLRNG, RANLUXCL, MWC64X). But i don't know whether it directly collect entropy from GPU or not.
[1]
https://dotneststatic.com/media/gpuday/GPUDay2019/talks/thursday/7_IstvanKiss.pdf, page 20