On some 32-bit platforms (at least on parisc), the compiler generates
a call to __divdi3() from the u32 by 3 division in
rkcanfd_timestamp_init(), which results in the following linker
error:

| ERROR: modpost: "__divdi3" [drivers/net/can/rockchip/rockchip_canfd.ko] undefined!

As this code doesn't run in the hot path, a 64 bit by 32 bit division
is OK, even on 32 bit platforms. Use an explicit call to div_u64() to
fix linking.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409072304.lCQWyNLU-lkp@intel.com/
Link: https://patch.msgid.link/20240909-can-rockchip_canfd-fix-64-bit-division-v1-1-2748d9422b00@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>