[CAN]: Move proto_{,un}register() out of spin-locked region

The implementation of proto_register() has changed so that it can now
sleep.  The call to proto_register() must be moved out of the
spin-locked region.

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>