use AO_FMT_NATIVE instead of AO_FMT_LITTLE in libao plugin
use AO_FMT_NATIVE instead of AO_FMT_LITTLE in libao plugin

use native format and let libao figure out endianness

Reviewed-by: Christopher Brannon <12dbcddb2a34235e759e3c56208f0d4ec028c34a@gmail.com>

razr/speechd,razr/speechd,razr/speechd,razr/speechd