Ecore: Use calloc() to initialize Ecore_Event_Key fully

Ecore: Use calloc() to initialize Ecore_Event_Key fully

Some fields (eg. data) may not be properly initialized.
Use calloc() instead of malloc() will ensure proper initialization
even if we add more fields.

These fields (data) would even be passed down to Evas as
Evas_Event_Key_Down for instance.