drm/amdkfd: fix clock counter retrieval for node without GPU

drm/amdkfd: fix clock counter retrieval for node without GPU

Currently if a user requests clock counters for a node without a GPU
resource we will always return EINVAL.

Instead if no GPU resource is attached, fill the gpu_clock_counter
argument with zeroes so that we may proceed and return valid CPU
counters.

Signed-off-by: Andres Rodriguez <[email protected]>
Signed-off-by: Felix Kuehling <[email protected]>
Reviewed-by: Oded Gabbay <[email protected]>
Signed-off-by: Oded Gabbay <[email protected]>