Please verify if the permission for multipath.conf is set as below
-rw-r--r--. 1 root root 3084 Aug 5 13:24 /etc/multipath.conf
If not then correct the permissions as above and then retry the installation
Ref: How to Manually Configure Disk Storage devices for use with Oracle ASM 11.2 and 12.1 on IBM: Linux on System z under RedHat 6 (Doc ID 1377392.1)
Vandana - Oracle
Are you using correct user and group (and permissions) for disks (directory and files that you created)?
Usually owner for Grid Infra is not oracle.
Check this (step 9):