can: m_can: make custom bittiming fields const

can: m_can: make custom bittiming fields const

commit daa278e1a9dbbf514ee714184eb50fdd1a71faae upstream.

The assigned timing structs will be defined a const anyway, so we can
avoid a few casts by declaring the struct fields as const as well.

Link: https://lore.kernel.org/all/4508fa4e639164b2584c49a065d90c78a91fa568.1636967198.git.matthias.schiffer@ew.tq-group.com
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>