mdesc: fix a missing-check bug in get_vdev_port_node_info()

[ Upstream commit 80caf43549e7e41a695c6d1e11066286538b336f ]

In get_vdev_port_node_info(), 'node_info->vdev_port.name' is allcoated
by kstrdup_const(), and it returns NULL when fails. So
'node_info->vdev_port.name' should be checked.

Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>