netapp-nvme: fix smdevices segfault in json output

netapp-nvme: fix smdevices segfault in json output

After the upgrade to libnvme, the NetApp plugin for smdevices
segfaults due to the wrong json object type as shown below:

nvme: json_object.c:1194: json_object_array_add:
Assertion `json_object_get_type(jso) == json_type_array' failed.
Aborted (core dumped)

Fix this by passing the appropriate json array type for smdevices.
Also include a couple of minor changes as well - add a newline to
the end of the json output, and then free the json root device.

Signed-off-by: Martin George <marting@netapp.com>
Tested-by: Clayton Skaggs <claytons@netapp.com>