can: at91_can: at91_set_bittiming(): demote register output to debug level

This message isn't really helpful for the general reader of the kernel
logs, so should not be printed with info level.

Link: https://lore.kernel.org/all/20231005-at91_can-rx_offload-v2-13-9987d53600e0@pengutronix.de


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