Btrfs: Properly setup root key while reading the root

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5accced..5a7e60d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -410,6 +410,7 @@
 	read_extent_buffer(l, &root->root_item,
 	       btrfs_item_ptr_offset(l, path->slots[0]),
 	       sizeof(root->root_item));
+	memcpy(&root->root_key, location, sizeof(*location));
 	ret = 0;
 out:
 	btrfs_release_path(root, path);