Wrong var on ContactBundle datagrid

[dainiusgliebus]

Summary
Lastname filters firstname

Steps to reproduce
crm/src/Oro/Bundle/ContactBundle/Resources/config/oro/datagrids.yml

contact-group-contacts-grid:
filters:
columns:
hasGroup:
data_name: hasGroup
type: boolean
firstName:
type: string
data_name: c.firstName
lastName:
type: string
data_name: c.firstName <<<<----- c.lastName

branches -> master, crm 4.2

[anyt]

Thank you for the report, @dainiusgliebus.
Internal ticket id #BB-20528.