Btrfs: use right root when checking for hash collision

btrfs_rename was using the root of the old dir instead of the root of the new
dir when checking for a hash collision, so if you tried to move a file into a
subvol it would freak out because it would see the file you are trying to move
in its current root.  This fixes the bug where this would fail

btrfs subvol create test1
btrfs subvol create test2
mv test1 test2.

Thanks to Chris Murphy for catching this,

Cc: [email protected]
Reported-by: Chris Murphy <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Chris Mason <[email protected]>

fs/btrfs/inode.c

@@ -7986,7 +7986,7 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 
 
 	/* check for collisions, even if the  name isn't there */
-	ret = btrfs_check_dir_item_collision(root, new_dir->i_ino,
+	ret = btrfs_check_dir_item_collision(dest, new_dir->i_ino,
 			     new_dentry->d_name.name,
 			     new_dentry->d_name.len);