Bug 29134: (follow-up) Specify which borrowernumber

Bug 29134: (follow-up) Specify which borrowernumber

When performing a search that includes permissions we need to specify we are comparing
the borrowers tabnle borrowernumber

To test:
1 - Browse to Admin->Funds
2 - Edit a fund
3 - Click '+ Add users'
4 - Attempt a search, no results
5 - Check plack-error.log
    C4::Utils::DataTables::Members::search(): DBI Exception: DBD::mysql::st execute failed: Column 'borrowernumber' in IN/ALL/ANY subquery is ambiguous at /kohadevbox/koha/svc/members/search line 80
6 - Apply patch
7 - Repeat 1-3
8 - search for 'a'
9 - Result!

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>