As Text::CSV is back in sync with Text::CSV_XS, you can shorten that a lot :)

#!/usr/bin/env perl

use 5.14.2;
use warnings;

use Text::CSV "csv";
use Data::Peek;

my $content = <<"EOC";
id;naaam;datum in dienst;functie
1;Jip;2001-04-14;Chef lege dozen
2;Janneke;2013-10-01;Miep kraak
EOC

my @medewerkers;
open my $FH, "<:encoding(utf8)", \$content or
    die "could not open result as file-handle: $!";
my $csv = Text::CSV_XS->new ({
    sep_char  => ";",
    binary    => 1,
    auto_diag => 1,
    });
$csv->header ($FH, { detect_bom => 1 });
while (my $row = $csv->getline_hr ($FH)) {
    push @medewerkers, $row;
    }
close $FH;
DDumper \@medewerkers;
[download]

[
    {   'datum in dienst' => '2001-04-14',
        functie          => 'Chef lege dozen',
        id               => '1',
        naaam            => 'Jip'
        },
    {   'datum in dienst' => '2013-10-01',
        functie          => 'Miep kraak',
        id               => '2',
        naaam            => 'Janneke'
        }
    ]
[download]

Now shorten that to

#!pro/bin/perl

use 5.14.2;
use warnings;

use Text::CSV "csv";
use Data::Peek;

my $content = <<"EOC";
id;naaam;datum in dienst;functie
1;Jip;2001-04-14;Chef lege dozen
2;Janneke;2013-10-01;Miep kraak
EOC

DDumper csv (in => \$content, bom => 1);
[download]

Or, if you want to be more explicit

Which would reduce your function to

sub csv_content {
    my $res = shift;
    return csv (in => \$res->content, bom => 1, sep => ";");
    } # csv_content
[download]

Add some error handling and you're done :)