[faiproject/fai] 27c726: do not try to stop raid sync for raid0

[Mrfai]

  Branch: refs/heads/master
  Home:   https://github.com/faiproject/fai
  Commit: 27c7267badb46918ef669c84aef0275a9fc438c0
      https://github.com/faiproject/fai/commit/27c7267badb46918ef669c84aef0275a9fc438c0
  Author: Thomas Lange <lange at debian.org>
  Date:   2022-01-21 (Fri, 21 Jan 2022)

  Changed paths:
    M lib/setup-storage/Commands.pm

  Log Message:
  -----------
  do not try to stop raid sync for raid0

echo frozen > ... will lead to this error
sh: line 1: /sys/block/md2/md/sync_action: Permission denied
echo frozen > /sys/block/md2/md/sync_action had exit code 1