bug#64745: [guix-past] channel derivation broken after recent u-boot update

[Maxim Cournoyer]

Hello,

It appears that the Guix-Past channel now fails to build like so:

--8<---------------cut here---------------start------------->8---
substitute: ^Msubstitute: ESC[Kupdating substitutes from 
'https://ci.guix.gnu.org'...   0.0%^Msubstitute: ESC[Kupdating substitutes from 
'https://ci.guix.gnu.org'... 100.0%
substitute: ^Msubstitute: ESC[Kupdating substitutes from 
'https://bordeaux.guix.gnu.org'...   0.0%^Msubstitute: ESC[Kupdating 
substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
@ build-started /gnu/store/5gxx0xnrncdg5rsi00j4bvy4frxpd466-guix-past.drv - 
x86_64-linux 
/var/log/guix/drvs/5g//xx0xnrncdg5rsi00j4bvy4frxpd466-guix-past.drv 4536
(repl-version 0 1 1)
(exception unbound-variable (value #f) (value "Unbound variable: ~S") (value 
(crust-pine64-plus)) (value #f))
builder for `/gnu/store/5gxx0xnrncdg5rsi00j4bvy4frxpd466-guix-past.drv' failed 
to produce output path `/gnu/store/hwfy6kbh8q7v9ljam99gfzaz46lf3i8z-guix-past'
@ build-failed /gnu/store/5gxx0xnrncdg5rsi00j4bvy4frxpd466-guix-past.drv - 1 
builder for `/gnu/store/5gxx0xnrncdg5rsi00j4bvy4frxpd466-guix-past.drv' failed 
to produce output path `/gnu/store/hwfy6kbh8q7v9ljam99gfzaz46lf3i8z-guix-past'
--8<---------------cut here---------------end--------------->8---

I suspect it's caused by the commit
ed5dc3a25d858a394bb7db937a51d866c3cdc6ed ("gnu: u-boot: Add crust
firmware to pinebook, pine64_plus and pine64-lts."), although I don't
understand why.

-- 
Thanks,
Maxim