~2% faster dts decoding overall.

                    cortex-a57   cortex-a53
dca_decode_hf_c:    474.8        1659.9
dca_decode_hf_neon: 225.2         301.1
dca_lfe_fir0_c:     913.2        1537.7
dca_lfe_fir0_neon:  286.8         451.9
dca_lfe_fir1_c:     848.7        1711.5
dca_lfe_fir1_neon:  387.1         506.4