Fix repeating data id length 11 not 6

In list.php id fields are created int(11) as per Joomla standard.

Here for repeated fields they are int(6) which leads to field changes
when you later edit a repeated field.
Merge pull request #751 from Sophist-UK/sophist_fix_repeating_data_id_length

Fix repeating data id length 11 not 6