ASoC: zx-i2s: fix harsh noise with 16-bit audio

The audio parameter setup in zx_i2s_hw_params() works fine with 32-bit
samples, but for 16-bit ones, all we can hear is harsh noises.
As suggested by vendor driver code, DMA burst size and TS width should
always be 32 bits, no matter audio sample is 16-bit or 32-bit.

Follow the suggestion above to fix the harsh noise issue seen with
16-bit audio samples.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>