modernizes for loop in cmd/, internal/ (#21309)

cmd/erasure-multipart.go

@@ -1481,7 +1481,7 @@ func (er erasureObjects) CompleteMultipartUpload(ctx context.Context, bucket str
 		}
 	}
 
-	for i := 0; i < len(onlineDisks); i++ {
+	for i := range len(onlineDisks) {
 		if onlineDisks[i] != nil && onlineDisks[i].IsOnline() {
 			// Object info is the same in all disks, so we can pick
 			// the first meta from online disk