can: m_can: Constify struct m_can_ops

can: m_can: Constify struct m_can_ops

'struct m_can_ops' is not modified in these drivers.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
   4806	    520	      0	   5326	   14ce	drivers/net/can/m_can/m_can_pci.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
   4862	    464	      0	   5326	   14ce	drivers/net/can/m_can/m_can_pci.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/all/a17b96d1be5341c11f263e1e45c9de1cb754e416.1719172843.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>