can: sja1000: sja1000_err(): make use of sja1000_get_berr_counter() to read error...

can: sja1000: sja1000_err(): make use of sja1000_get_berr_counter() to read error counters

This is a preparation patch to make use of can_state_get_by_berr_counter()
which works on a struct can_berr_counter.

Reuse the existing function sja1000_get_berr_counter() to read the error
counters into a struct can_berr_counter.

Reviewed-by: Michael Tretter <m.tretter@pengutronix.de>
Link: https://patch.msgid.link/20260123-sja1000-state-handling-v2-1-687498087dad@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>