Partition process: fix handling loop devices

[igorpecovnik]

Description

When adding several improvements to the cryptoroot handling, we accidentally broke stability of handling loop devices. Partially reverting #7527 seems to be a solution.

@swissiety Check if there are no regression on the cryptoroot side.

How Has This Been Tested?

• Build nightly images
• Test one of the images on hardware

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[swissiety]

• builds with lvm, crypt, lvm+crypt

successful 1st boot on rock3a with:

• lvm
• crypt
• lvm+crypt

"It works on my machine" ;-) thx for fixing it!

[igorpecovnik]

It works on my machine

Good enough ;)