can: softing: softing_netdev_open(): fix error handling

If softing_netdev_open() fails, we should call close_candev() to avoid
reference leak.

Fixes: 03fd3cf5

 ("can: add driver for Softing card")
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Acked-by: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
Link: https://lore.kernel.org/r/20201202151632.1343786-1-zhangqilong3@huawei.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20201204133508.742120-2-mkl@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>