can: tcan4x5x: remove not needed casts to struct tcan4x5x_priv *

The struct m_can_classdev::device_data is a void pointer, so there's no
need to cast it to struct tcan4x5x_priv *, when assigning the struct
tcan4x5x_priv pointer.

This patch removes the not needed casts from the tcan4x5x driver.

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