can: peak_usb: pcan_usb_decode_error(): upgrade handling of bus state changes

This patch updates old code by using the can_change_state() function
published since by the socket-can module.

In particular, this new code better manages the change of bus state by
also using the value of the error counters that the driver now
systematically asks for when initializing the channel.

Link: https://lore.kernel.org/r/20210715142842.35793-1-s.grosjean@peak-system.com


Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>