can: remove obsolete get_canfd_dlc() macro

The macro was always used together with can_dlc2len() which sanitizes the
given dlc value on its own.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20201110101852.1973-4-socketcan@hartkopp.net


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