Fixed incorrect usage of clGetDeviceIDs num_devices

[paulfradgley]

clGetDeviceIDs 'num_devices' output parameter is described as:

num_devices returns the number of OpenCL devices available that match device_type.

but the test_events out_of_order_event_waitlist_multi_queue_multi_device test expects that after calling: clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL, 2, two_device_ids, &number_returned);

the content of number_returned needs to be 2, but it should be valid to return a larger number.