In 11g R2 Clusterware configurations the OCR is located in ASM disk, that’s why ASM can’t be shutdown while the cluster is running. You have to shutdown your cluster in order to shutdown ASM instance.
Oracle support note 984663.1
Here’s a good blog about this:
Example, how to shutdown ASM instance on node ol5-112-rac1:
Shutdown RAC1 instance first:
Then proceed to shutdown cluster (root required):
At this point ASM & Cluster Ready Services managed resources are down.
In order to start them again just need to issue: