can: at91_can: at91_irq_err(): rename to at91_irq_err_line()

This is a cleanup patch, no functional change intended.

The function at91_irq_err() only handles the CAN line errors, so
rename it accordingly to at91_irq_err_line().

Link: https://lore.kernel.org/all/20231005-at91_can-rx_offload-v2-21-9987d53600e0@pengutronix.de


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