asus: fix charge-upto script

[shinishiho]

Description of changes

Added shebang and fix script argument. Fixed:

• Error while executing:

/run/current-system/sw/bin/charge-upto: line 1: /sys/class/power_supply/BAT?/charge_control_end_threshold: No such file or directory

• Incorrect argument: ${0}is the script name.

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input