can: flexcan: 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. All other register
programming outputs in the flexcan driver already use the debug level.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>