Btrfs: reserve space for O_TMPFILE orphan item deletion

btrfs_link() calls btrfs_orphan_del() if it's linking an O_TMPFILE but
it doesn't reserve space to do so. Even before the removal of the
orphan_block_rsv it wasn't using it.

Fixes: ef3b9af50bfa ("Btrfs: implement inode_operations callback tmpfile")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -6658,8 +6658,9 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
 	 * 2 items for inode and inode ref
 	 * 2 items for dir items
 	 * 1 item for parent inode
+	 * 1 item for orphan item deletion if O_TMPFILE
 	 */
-	trans = btrfs_start_transaction(root, 5);
+	trans = btrfs_start_transaction(root, inode->i_nlink ? 5 : 6);
 	if (IS_ERR(trans)) {
 		err = PTR_ERR(trans);
 		trans = NULL;