ecasound 2.8.1: Fix ruby support with explicit --enable-rubyecasound

Change formula to always pass explicit --enable-rubyecasound=<yes|no>
so it works regardless of the ecasound configure's default behavior
for --enable-ruby. Formula was assuming default was no, but default was
actually yes, so the ruby stuff got built even when --with-ruby was
not supplied, which could break the build when attempting to install
in to /Library/Ruby. Fixes #19357.