can: rockchip_canfd: rkcanfd_timestamp_init(): rework delay calculation

Rework the delay calculation to only require a single 64-bit division.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[mkl: port to on-top of existing 32-bit division fix]
Link: https://patch.msgid.link/20240911-can-rockchip_canfd-fixes-v1-1-5ce385b5ab10@pengutronix.de


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