can: mcp251xfd: mcp251xfd_open(): request IRQ as shared

The driver's IRQ handler supports shared IRQs, so request a shared IRQ
handler.

Link: https://lore.kernel.org/r/20210724205212.737328-1-mkl@pengutronix.de


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