can: mcp251xfd: mcp251xfd_chip_stop(): convert to a void function

can: mcp251xfd: mcp251xfd_chip_stop(): convert to a void function

The mcp251xfd_chip_stop() function tries the best to stop the chip and
put it into sleep mode. It continues, even if some intermediate steps
fail. As none of the callers use the return value, let this function
return void.

Link: https://lore.kernel.org/all/20220207131047.282110-6-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>