Btrfs: insert_new_root: Fix lock type of the extent buffer.

btrfs_alloc_tree_block() returns an extent buffer on which a blocked lock has
been taken. Hence assign the appropriate value to path->locks[level].
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.c

@@ -3380,7 +3380,7 @@ static noinline int insert_new_root(struct btrfs_trans_handle *trans,
 	add_root_to_dirty_list(root);
 	extent_buffer_get(c);
 	path->nodes[level] = c;
-	path->locks[level] = BTRFS_WRITE_LOCK;
+	path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 	path->slots[level] = 0;
 	return 0;
 }