AESinkALSA: Workaround alsa-lib buffer overflow in snd_pcm_chmap_print

Provide a double-length buffer for snd_pcm_chmap_print(), which the
buggy versions cannot overflow.

http://trac.kodi.tv/ticket/15641
http://mailman.alsa-project.org/pipermail/alsa-devel/2014-December/085815.html
Merge pull request #6065 from anssih/fix/AE-ticket15641

AESinkALSA: Workaround alsa-lib buffer overflow in snd_pcm_chmap_print