libafscp: makefile install rule update

Change the makefile install rules to install the header
file from the libafscp directory, and not the top level
include directory to make the install rules consistent
with the rest of the tree.

Change-Id: Ia06c29e72f7005569f2d11d3d0f6691413e0eeec
Reviewed-on: http://gerrit.openafs.org/10514
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>