btrfs: alloc_chunk: do not refurbish num_bytes

The variable num_bytes is used to store the chunk length of the chunk
that we're allocating. Do not reuse it for something really different in
the same function.
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NHans van Kranenburg <hans.van.kranenburg@mendix.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -4869,10 +4869,9 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	if (ret)
 		goto error_del_extent;
 
-	for (i = 0; i < map->num_stripes; i++) {
-		num_bytes = map->stripes[i].dev->bytes_used + stripe_size;
-		btrfs_device_set_bytes_used(map->stripes[i].dev, num_bytes);
-	}
+	for (i = 0; i < map->num_stripes; i++)
+		btrfs_device_set_bytes_used(map->stripes[i].dev,
+				map->stripes[i].dev->bytes_used + stripe_size);
 
 	atomic64_sub(stripe_size * map->num_stripes, &info->free_chunk_space);