[FIX] crm: From 'Scheduled Calls', if we open the 'Opportunity/Lead' by ...

...clicking on the many2one link in non-editable mode(or in editable mode of form view by clicking on that field), it always open that record in lead form view(crm_case_form_view_leads) even if it is an opportunity. (Maintenance Case: 608493)

Steps to reproduce the issue:
1) Create an opportunity,
2) Schedule a call(make sure you select the action as "Schedule a call"),
3) Go to the "Sales/Phone Calls/Scheduled Calls" and open the call(created in step 2) in the form view in editable mode,
4) Open the "Lead/Opportunity" many2one record.

Current behavior: The opportunity opened as "Leads"(in "crm_case_form_view_leads" view).

Expected behavior: If it's a "lead" then open it in "crm_case_form_view_leads" view or if it's an "opportunity" then open it in "crm_case_form_view_oppor".
Use `self.pool['ir.model.data']` not `self.pool.get('ir.model.data')`