libadmin: add header file deps

Add the missing header file dependencies to the library targets.
This is needed for parallel make.

Change-Id: I60d60e68ef808a62b4063a6106672f5178c1b605
Reviewed-on: http://gerrit.openafs.org/10726
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>