fix alsa mixer calculations
fixes #1222
I hope, this fixes the issues mentioned with alsa and alsa_linear. Please note that one of them will behave weirdly on your system depending on, whether your alsa control is linear or not. (At least that is what I assume based on my experience...) However, they should both be able to reach 0% and not be reset when hitting play.
Any testing is appreciated. (maybe @Arbee4ever?)
I'd be happy to test this, but I run spotifyd on a Raspberry Pi (2B), which is currently suffering from this issue (and have switched to using softvol) and I am not sure how to get this on there. I setup by just downloading the Armv6 binary. Do I just compile it on the Pi?
@Ionshard that would be great. You can indeed just compile on the Pi, but you might need some packages (see the docs) and it is going to take a long time.