CL_INVALID_BUFFER_SIZE error on macOS running with --opencl flag
Bug: unable to use opencl on macos with intel graphics. 

**To Reproduce**
build on macos bigsur from latest git pull

**Required data**
```
 |  # | GPU |  BUS ID | INTENSITY | WSIZE | MEMORY | NAME
|  0 |   0 |     n/a |       320 |     8 |    640 | Iris Pro
[2021-10-09 22:47:58.462]  opencl   error CL_INVALID_BUFFER_SIZE when calling clCreateBuffer with buffer size 2181038080
[2021-10-09 22:47:59.443]  cpu      READY threads 3/3 (3) huge pages 0% 0/3 memory 6144 KB (6754 ms)
[2021-10-09 22:47:59.447]  opencl   thread #0 failed with error RandomX dataset is not available
[2021-10-09 22:47:59.453]  opencl   thread #0 self-test failed
[2021-10-09 22:47:59.453]  opencl   disabled (failed to start threads)

```

--cpu-max-threads-hint=100 -k --nicehash  --print-time==5 --api-worker-id=xx --rig-id=xx --verbose  --cpu-no-yield  --cpu-priority=5   --randomx-1gb-pages   --randomx-mode=fast --opencl
 
 