[FIX] l10n_ch: fix bad field renaming in QR code generation

Originally introduced by https://github.com/odoo/odoo/commit/f3c1e6cfbe70f9dd37cc7c7b3b3464c5b9af280b



closes odoo/odoo#43474

X-original-commit: 3c85bed2
Signed-off-by: oco-odoo <oco-odoo@users.noreply.github.com>