can: m_can: let m_can_class_allocate_dev() allocate driver specific private data

This patch enhances m_can_class_allocate_dev() to allocate driver specific
private data. The driver's private data struct must contain struct
m_can_classdev as its first member followed by the remaining private data.

Link: https://lore.kernel.org/r/20201212175518.139651-7-mkl@pengutronix.de


Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>