modem/q6voiced: upgrade to 0_git20210408 (fix bad regression)

When I upgraded tinyalsa to the new 2.0.0 major release (with breaking changes) I failed to test q6voiced properly, even though I explicitly had to rebuild it against the new tinyalsa version (see !1941 (merged)).

In tinyalsa 2.0.0, calling pcm_open() does not automatically call pcm_prepare() anymore, which is responsible for actually starting any audio streams. This means that the old version of q6voiced is almost entirely broken - only by pure luck it's sometimes possible to get voice call audio working if you play other audio simultaenously while a voice call is active. This does not work for the microphone though.

The new q6voiced version now calls pcm_prepare() explicitly to fix this.

Note: There is no need to backport this since Alpine 3.13 still seems to have the old tinyalsa version.