net: at91_can: fix the code style issue about macro

Macros with complex values should be enclosed in parentheses

Link: https://lore.kernel.org/r/1624096589-13452-4-git-send-email-huangguangbin2@huawei.com


Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>