can: mcp251x: fix coccinelle warnings

drivers/net/can/spi/mcp251x.c:953:7-27: ERROR: Threaded IRQ with no primary handler requested without IRQF_ONESHOT

 Make sure threaded IRQs without a primary handler are always request with
 IRQF_ONESHOT

Generated by: scripts/coccinelle/misc/irqf_oneshot.cocci

CC: Stefano Babic <sbabic@denx.de>
CC: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>