[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

'partner_id': self.pool['hr.payslip.line']._get_partner_id(cr, uid, [line.id], credit_account=True, context=context)