Enable repair when checking exfat file systems

Quoting the commit message:

GParted's check operation is a check and if possible repair. For most
file system types GParted already requests that the file system is
repaired. fsck.exfat -y flag has been available since the first release
of exfatprogs 1.0.1 [1] so unconditionally add this.

[1] exfatprogs 1.0.1 fsck/fsck.c:main() case 'y':
https://github.com/exfatprogs/exfatprogs/blob/1.0.1/fsck/fsck.c#L1231