can: xilinx_can: mark bit timing constants as const

This patch marks the bit timing constants as const.

Fixes: c223da68 ("can: xilinx_can: Add support for CANFD FD frames")
Link: https://lore.kernel.org/all/20220317203119.792552-1-mkl@pengutronix.de


Cc: Appana Durga Kedareswara rao <appana.durga.rao@xilinx.com>
Cc: Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>