can: m_can: Use u32 for putidx

putidx is not an integer normally, it is an unsigned field used in
hardware registers. Use a u32 for it.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/all/20240207093220.2681425-9-msp@baylibre.com


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