The package description https://packages.gentoo.org/packages/dev-embedded/rpi-eeprom contains a space in the link to the upstream repo in the metadata of that package. Following the link results in a 404 Not Found error.
Already fixed in https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=f987e0bf9ae93b85af64e1990b5971348b8c2949 so I think p.g.o is to blame?
There was an issue that the upstream information of a package wasn't getting updated. Fixed for separate bug which also fixed here. Thank you for the report