can: at91_can: use a consistent indention

Convert the driver to use a consistent indention of one space after
defines and in enums. That makes it easier to add new defines, which
will be done in the coming patches.

Link: https://lore.kernel.org/all/20231005-at91_can-rx_offload-v2-2-9987d53600e0@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>