Bug 28554: In Koha::AuthorisedValues sort by description

Bug 28554: In Koha::AuthorisedValues sort by description

In itemsearch form, there are several filters build with authorized values.
There values should be sorted by description.

Test plan :
1) Create several values and descriptions in authorized values LOC
2) Go to itemsearch
3) See filter by location sorts on description and not on value

Seems change in search_by_marc_field can not be tested in interface

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>