Bug 20282: Match course reserve on holdingbranch

Bug 20282: Match course reserve on holdingbranch

To test:
1 - Add a course (Course Reserves)
2 - Add an item to the course
3 - Ensure to change the holding branch for the course reserve
4 - Modify the course item
5 - Note the dropdwn for holding branch is unset
6 - Apply patch
7 - Modify the course item
8 - Dropdown should be correctly populated

Signed-off-by: Maksim Sen <maksim.sen@inlibro.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>