I had done the following and now it is resolved:
1. srvctl config database -d <dbname> -a
2. From the dependencies I found that this diskgroup is listed.
3. Took the list of diskgroup (from dependencies), removed this diskgroup entry and ran the following command:
srvctl modify database -d <dbname> -a "data_dg1, data_dg2, data_dg3"
4. started the instance and it worked