drm/amdkfd: Short cut for kfd_wait_on_events without waiting

If kfd_wait_on_events can return immediately, we don't need to populate
the wait list and don't need to enter the sleep-loop.

Signed-off-by: Sean Keely <sean.keely@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>