Dropbear key files go in etc/dropbear, not etc/ssh
Thanks again to Adrian Grigo http://lists.cross-lfs.org/pipermail/clfs-dev-cross-lfs.org/2011-April/000963.html
The current bootscripts expect ${CLFS}/etc/dropbear not ${CLFS}/etc/ssh to be the place to find Dropbear key files and other configuration files.