[rear-devel] [rear/rear] 330230: Update 300_create_grub.sh

[Johannes Meixner]

  Branch: refs/heads/jsmeix-improve-GRUB2-USB
  Home:   https://github.com/rear/rear
  Commit: 3302309ae525f067e5693386fd4db2faf06e2ead
      https://github.com/rear/rear/commit/3302309ae525f067e5693386fd4db2faf06e2ead
  Author: Johannes Meixner <jsmeix at suse.com>
  Date:   2021-07-21 (Wed, 21 Jul 2021)

  Changed paths:
    M usr/share/rear/output/USB/Linux-i386/300_create_grub.sh

  Log Message:
  -----------
  Update 300_create_grub.sh

Use GRUB2_SET_USB_ROOT instead of grub2_set_usb_root for that global variable