Bug 29435: include missing subroutine from C4::AuthoritiesMarc

Bug 29435: include missing subroutine from C4::AuthoritiesMarc

The OPAC authority details page is broken when the 'AuthDisplayHierarchy'
System Preference is set to 'Enable',

This patch fixes that.

Test plan:
1) Set AuthDisplayHierarchy to 'Enable' and try to view the details
   page of an authority in the OPAC -- the page is broken.
2) Apply this patch.
3) Refresh the page; this time the authority details are displayed.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>