FIX: InfluxDB NSM Disk Usage visualization

[dougburks]

Reported at #10501 (reply in thread) and duplicated on a fresh 2.4.2 installation.

[jertel]

Validation of fix follows.

This is from an ISO install:

correlates with df:

[onion@securityonion ~]$ df -h
Filesystem               Size  Used Avail Use% Mounted on
devtmpfs                 4.0M     0  4.0M   0% /dev
tmpfs                    7.7G   20K  7.7G   1% /dev/shm
tmpfs                    3.1G   11M  3.1G   1% /run
/dev/mapper/system-root   83G   21G   63G  25% /
/dev/mapper/system-nsm   173G   11G  163G   6% /nsm
/dev/sda2                507M  211M  297M  42% /boot
tmpfs                    1.6G     0  1.6G   0% /run/user/1000
tmpfs                    1.6G     0  1.6G   0% /run/user/0
tmpfs                    1.6G     0  1.6G   0% /run/user/939