fs/affs: release old buffer head on error path

commit 70779b897395b330ba5a47bed84f94178da599f9 upstream.

The reference count of the old buffer head should be decremented on path
that fails to get the new buffer head.

Fixes: 6b465766 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>