You simply need to include the sound driver module in /etc/modules:
sudo -i
nano /etc/modules
After the line vchiq add snd_bcm2835 so the file looks like:
# /etc/modules: kernel modules to load at boot time
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
# Parameters can be specified after the module name.

After editing /etc/modules you should reboot