The reference count of the old buffer head should be decremented on path
that fails to get the new buffer head.
Fixes: 6b4657667b ("fs/affs: add rename exchange")
CC: stable@vger.kernel.org # 4.14+
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: David Sterba <dsterba@suse.com>