For storing Voting disks in ASM,we require minimum of three disks or three failgroups for Normal Redundancy diskgroup.
The number of voting files you can store in a particular Oracle ASM disk group depends upon the redundancy of the disk group.
ASM puts each voting disk in its own failure group within the disk group.
solutions: change Oracle asm disk group redudancy.
A normal redundancy disk group must contain at least two failure groups but if you are storing your voting disks on Oracle ASM, then a normal redundancy disk group must contain at least three failure groups.