invalid prefix log message should quote the prefix

As reported in https://lists.isc.org/pipermail/bind-users/2022-March/105833.html

The problem log message was:

Mar 11 18:14:27 tilapia named[9206]: /etc/bind/named.conf.options:40: invalid prefix, bits [64..71] must be zero

It fails to quote the invalid prefix, so that the reader can easily see which of multiple prefixes is erroneous.