I've encountered this too and have a iQaudio DAC that is no longer detected and I don't get any sound. Also noticed errors regarding bcm2835 on a couple of PiZeroW's too but thats a separate issue.
Is there an equivalent of
http://arch.archlinux.org/ where older packages are available so I can try rolling things back?
I only keep the last two packages to avoid filling up /var/cache/pacman/pkg/ and don't have old kernels/headers.