Bug 21448: Fix copy repeated subfields when linking an authority with 6xx

Bug 21448: Fix copy repeated subfields when linking an authority with 6xx

The reported issue was:
On field 606, if I use an Authority with multiple "x" subfields, it will
add just the first "x"

Error in the logs:
Odd number of elements in anonymous hash at /home/vagrant/kohaclone/authorities/blinddetail-biblio-search.pl line 97.

We should pass a ref (!), caused by
  commit a7df1f9f8eb9ed16246964d94dd8a69b756b6551
  Bug 18904: (follow-up) Retrieve subfield in the order they are stored

Test plan:
Edit an authority and add several $x to 600
Link this authority to a bibliographic record
=> Without this patch only the first subfield is copied
=> With this patch applied they are all copied

Signed-off-by: José Anjos <joseanjos@gmail.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>