SMART plugin: initialize struct passed to `ioctl(2)`.

SMART plugin: initialize struct passed to `ioctl(2)`.

Valgrind is complaining about a conditional jump based on uninitialized
memory:

```
==66462== Conditional jump or move depends on uninitialised value(s)
==66462==    at 0x10C500: smart_read_nvme_intel_disk (in /__w/collectd/collectd/test_plugin_smart)
==66462==    by 0x10D366: test_x (in /__w/collectd/collectd/test_plugin_smart)
==66462==    by 0x10D638: main (in /__w/collectd/collectd/test_plugin_smart)
```

This may be due to the `struct nvme_additional_smart_log` being
uninitialized when it's being passed to `ioctl(2)`.

This there, this removed an unnecessary level of indentation.