drm/amdkfd: fix null queue check on debug setting exceptions

Null check should be done on queue struct itself and not on the
process queue list node.
Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_debug.c

@@ -1097,7 +1097,7 @@ void kfd_dbg_set_enabled_debug_exception_mask(struct kfd_process *target,
 
 	pqm = &target->pqm;
 	list_for_each_entry(pqn, &pqm->queues, process_queue_list) {
-		if (!pqn)
+		if (!pqn->q)
 			continue;
 
 		found_mask |= pqn->q->properties.exception_status;