ASoC: codecs: msm8916-wcd-analog: fix micbias level

The macro used to set the microphone bias level causes the
snd_soc_write() call to overwrite other fields in the CDC_A_MICB_1_VAL
register. The macro also does not return the proper level value
to use. This fixes this by preserving all bits from the register
that are not the level while setting the level.

Signed-off-by: Jean-François Têtu <jean-francois.tetu@savoirfairelinux.com>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>