drm/amdkfd: allow unregister process with queues

Sometimes we might unregister process that have queues, because we couldn't
preempt the queues. Until now we blocked it with BUG_ON but instead just
print it as debug.

Reviewed-by: Ben Goz <ben.goz@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>