Bug 28162: fix doubled scalar sigil

Bug 28162: fix doubled scalar sigil

TEST PLAN:

1 Set up some patron extended attributes
2 Make sure you check 'Display in OPAC' and 'Editable in OPAC'
3 Go to self registration and attempt to register
4 you get an error ( Not a SCALAR reference at /kohadevbox/koha/opac/opac-memberentry.pl line 110 )
5 Apply patch
6 repeat steps 1-3, ther should be no error now

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