Fix for loop over value array range issue. (#2187)

plugins/inputs/system/ps.go

@@ -73,7 +73,10 @@ func (s *systemPS) DiskUsage(
 	var usage []*disk.UsageStat
 	var partitions []*disk.PartitionStat
 
-	for _, p := range parts {
+	for i := range parts {
+
+		p := parts[i]
+
 		if len(mountPointFilter) > 0 {
 			// If the mount point is not a member of the filter set,
 			// don't gather info on it.