Loop over multiple UPS's does not interate over individual values

[JPSteindlberger]

Although having configured multiple UPS's in NUT, in MQTT I found unique values for all those UPS's. For my purpose I fixed it in pkg/nut_client/nut_client.go this way:

for num := range upsList {
- upsVariables, err := upsList[0].GetVariables()
+ upsVariables, err := upsList[num].GetVariables()
if err != nil {

But as I'm not a Go developer I cannot tell whether this has negative impact to the error handling of this block. There might be a reason for using upsList[0] instead of upsList[num]