[REF][8.0][hr_payroll_account] Get partner_id with a function to inheritable case

Proposal to add a REF - More info here: https://github.com/odoo/odoo/issues/3274
OPW ticket 616565

Replace this by something like 
```
if credit_account:
    res[payslip_line.id] = (payslip_line.salary_rule_id.register_id.partner_id or ayslip_line.salary_rule_id.account_credit.type in ('receivable', 'payable')) and partner_id or False
else:
    res[payslip_line.id] = (payslip_line.salary_rule_id.register_id.partner_id or ayslip_line.salary_rule_id.account_debit.type in ('receivable', 'payable')) and partner_id or False
```