fix: correctly check nvidia MIG mode status for process utilization

[Henry-ZHR]

On common GPUs, like RTX:

$ nvidia-smi --query-gpu=mig.mode.current
mig.mode.current
[N/A]

Process utilization OK

On A100:

$ nvidia-smi --query-gpu=mig.mode.current
mig.mode.current
Disabled
Disabled
...

But no process utilization available

This PR should bring process utilization back when MIG disabled

[Syllo]

Nice catch of the double negation, thank you!