staging: vc04_services: Fix wrong early return in next_service_by_instance()

If kref_get_unless_zero() fails, we should keep looking for the
next service, since the callers of this function expect that a NULL
return value means there are no more.

Signed-off-by: Marcelo Diop-Gonzalez <marcgonzalez@google.com>
Link: https://lore.kernel.org/r/20200213194001.130110-1-marcgonzalez@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

@@ -252,11 +252,15 @@ next_service_by_instance(struct vchiq_state *state,
 	struct vchiq_service *service;
 
 	rcu_read_lock();
+	while (1) {
 		service = __next_service_by_instance(state, instance, pidx);
-	if (service && kref_get_unless_zero(&service->ref_count))
+		if (!service)
+			break;
+		if (kref_get_unless_zero(&service->ref_count)) {
 			service = rcu_pointer_handoff(service);
-	else
-		service = NULL;
+			break;
+		}
+	}
 	rcu_read_unlock();
 	return service;
 }