can: m_can: Rename m_can_priv to m_can_classdev

Rename the common m_can_priv class structure to m_can_classdev as this
is more descriptive.

Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Acked-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>