Fix: new lumi_fw.tar does not allow deletion

[Qianli-Ma]

Ran into an issue when running custom firmeware updates: It seems that newly downladed lumi_fw.tar has Cannot be modified (immutable) property set.

Added chattr command before deleting files to resolve.

[niceboygithub]

They are just warning and also help to the firmware is locked while updating the custom firmware.