[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".
The aim of this method is to return a correct view which can be get by a call to "get_object_reference(...)" of "ir.model.data" model and this method doesn't need context, and also, I thought this method wouldn't need any fancy stuff in future, like calling some function which would need context. So considering this I didn't pass the context to this method. But if you have some scenario that would have usage of context in this method then I will update the commit by passing it. What is your opinion on it?