[CAN]: Minor clean-ups

Remove unneeded variable.
Rename local variable error to err like in all other places.
Some white-space changes.

Signed-off-by: Urs Thuermann <urs.thuermann@volkswagen.de>
Signed-off-by: Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>