Otherwise BOs may wait for the fence indefinitely and never be destroyed.

v2: Signal the fence right after destroying queues to avoid unnecessary
    delaye-delete in kfd_process_wq_release
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: xinhui pan <xinhui.pan@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>