can: ti_hecc: remove priv->can.do_get_state() callback

This patch removes the priv->can.do_get_state() callback, as it just returns
priv->can.state. The callback's only user can_fill_info() has direct access to
priv->can.state.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>