Init script: Fix DAEMON var (Bins go to /usr/local/bin during install)

I recently installed shairport on my raspberry pi and wondered why it's telling me "<my hostname> not installed". Ignoring the fact, that this message is a bit confusing, I managed to get it running with this patch. 

`make install` copies the binary to `/usr/local/bin/shairport` while `DAEMON` is set to `/usr/bin/shairport`