grub_dpkg writes wrong device into debconf

This bug was originally filed in Launchpad as [LP: #1993503](https://bugs.launchpad.net/cloud-init/+bug/1993503)

Launchpad details

affected_projects = ['subiquity']

assignee = None

assignee_name = None

date_closed = None

date_created = 2022-10-19T09:31:46.547690+00:00

date_fix_committed = None

date_fix_released = None

id = 1993503

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1993503

milestone = None

owner = danielky

owner_name = Daniel Krambrock

private = False

status = triaged

submitter = danielky

submitter_name = Daniel Krambrock

tags = []

duplicates = []

_Launchpad user **Daniel Krambrock(danielky)** wrote on 2022-10-19T09:31:46.547690+00:00_

After auto-installing ubuntu 22.04 onto a LV on a mdraid 1 with two disks cc_grub_dpkg overrides the correct `grub-pc/install_devices` debconf entry with a false one on first boot:

```
~# debconf-show grub-pc | grep grub-pc/install_devices:
* grub-pc/install_devices: /dev/disk/by-id/dm-name-vg0-lv_root
```

This breaks grub updates.