ASoC: msm8916-wcd-analog: Fix RX1 selection in RDAC2 MUX

ASoC: msm8916-wcd-analog: Fix RX1 selection in RDAC2 MUX

According to the PM8916 Hardware Register Description,
CDC_D_CDC_CONN_HPHR_DAC_CTL has only a single bit (RX_SEL)
to switch between RX1 (0) and RX2 (1). It is not possible to
disable it entirely to achieve the "ZERO" state.

However, at the moment the "RDAC2 MUX" mixer defines three possible
values ("ZERO", "RX2" and "RX1"). Setting the mixer to "ZERO"
actually configures it to RX1. Setting the mixer to "RX1" has
(seemingly) no effect.

Remove "ZERO" and replace it with "RX1" to fix this.

Fixes: 1e90dab1850e ("ASoC: codecs: Add msm8916-wcd analog codec")
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20191020153007.206070-1-stephan@gerhold.net
Signed-off-by: Mark Brown <broonie@kernel.org>