fix: Merge() should merge and return a copy (#11714)

fixes #11713

pkg/madmin/info-commands.go

@@ -97,14 +97,15 @@ func (d1 BackendDisks) Merge(d2 BackendDisks) BackendDisks {
 	if len(d2) == 0 {
 		d2 = make(BackendDisks)
 	}
+	var merged = make(BackendDisks)
 	for i1, v1 := range d1 {
 		if v2, ok := d2[i1]; ok {
-			d2[i1] = v2 + v1
+			merged[i1] = v2 + v1
 			continue
 		}
-		d2[i1] = v1
+		merged[i1] = v1
 	}
-	return d2
+	return merged
 }
 
 // StorageInfo - Connect to a minio server and call Storage Info Management API