can: c_can: remove unnecessary blank lines and add suggested ones

This patch removes unnecessary blank lines and add suggested ones, so
that checkpatch doesn't complain anymore.

Link: https://lore.kernel.org/r/20210304154240.2747987-3-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>