Fix wrong path to asdf data directory

What does this Merge Request do?

Fixes wrong path to asdf data directory. Before this change running

make bootstrap
gdk install

failed if asdf had been installed with a package manager.

Closes #1085 (closed)

I'm submitting this as part of the quarterly GitLab Hackathon

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.