can: at91_can: at91_irq_err_line(): make use of can_change_state() and can_bus_off()

can: at91_can: at91_irq_err_line(): make use of can_change_state() and can_bus_off()

The driver implements a hand crafted CAN state handling. Update the
driver to make use of can_change_state(), introduced in ("can: dev:
Consolidate and unify state change handling")

Also switch from hand crafted CAN bus off handling to can_bus_off():
In case of a bus off, abort all pending TX requests, switch off the
device and let can_bus_off() handle the device restart.

Link: https://lore.kernel.org/all/20231005-at91_can-rx_offload-v2-24-9987d53600e0@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>