topology: decode: Fix channel map memory allocation

topology: decode: Fix channel map memory allocation

Memory allocated on the stack was referenced outside of the function scope
caused undefined behaviour.

Signed-off-by: Piotr Maziarz <piotrx.maziarz@linux.intel.com>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Reviewed-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>