[FIX] mrp: write with multiple workorders in self

This PR odoo/odoo#97805 wrongly assumed that
self contained a single workorder. This would raise an error if there
were multiple records in self.

Solution:
Modify calls on `self` to `workorder` (as we already iterate through
them)

closes odoo/odoo#101580

Signed-off-by: William Henrotin (whe) <whe@odoo.com>

addons/mrp/models/mrp_workorder.py

@@ -357,13 +357,13 @@ def write(self, values):
                     raise UserError(_('The planned end date of the work order cannot be prior to the planned start date, please correct this to save the work order.'))
                 if 'duration_expected' not in values:
                     if 'date_planned_start' in values and 'date_planned_finished' in values:
-                        computed_finished_time = self._calculate_date_planned_finished(start_date)
+                        computed_finished_time = workorder._calculate_date_planned_finished(start_date)
                         values['date_planned_finished'] = computed_finished_time
                     elif 'date_planned_start' in values:
-                        computed_duration = self._calculate_duration_expected(date_planned_start=start_date)
+                        computed_duration = workorder._calculate_duration_expected(date_planned_start=start_date)
                         values['duration_expected'] = computed_duration
                     elif 'date_planned_finished' in values:
-                        computed_duration = self._calculate_duration_expected(date_planned_finished=end_date)
+                        computed_duration = workorder._calculate_duration_expected(date_planned_finished=end_date)
                         values['duration_expected'] = computed_duration
                 # Update MO dates if the start date of the first WO or the
                 # finished date of the last WO is update.