ASoC: Leave input audio data bit length settings untouched in wm8711_set_dai_fmt

Current implementation in wm8711_set_dai_fmt always clear BIT[3:2]
(the Input Audio Data Bit Length Select) of WM8711_IFACE(07h) register.
Input Audio Data Bit Length Select bits are set by wm8711_hw_params,
we should leave BIT[3:2] untouched in wm8711_set_dai_fmt.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@kernel.org