net: at91_can: use BIT macro

This patch uses the BIT macro for setting individual bits,
to fix the following checkpatch.pl issue:
CHECK: Prefer using the BIT macro.

Link: https://lore.kernel.org/r/1624096589-13452-5-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>