build.sh: Set the path for radio files in vendor repo properly

Description

build.sh: Set the path for radio files in vendor repo properly

Issue(s)

https://gitlab.e.foundation/e/devices/backlog/-/issues/1242

Test procedures

• Ensure IMG & QFIL zips on v1-u have the firmware bundled inside.
• https://gitlab.e.foundation/e/priv/os/build/-/pipelines/463615

Check list

• Self review
• Test procedure explained
• Tested on fresh install
• Tested applied as an update
• License
• Internal documentation
• User documentation