can: use __dev_get_by_index instead of dev_get_by_index to find interface

As cgw_create_job() is always under rtnl_lock protection,
__dev_get_by_index() instead of dev_get_by_index() should be used to
find interface handler in it having us avoid to change interface
reference counter.

Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>