ASoC: msm8916-wcd-digital: fix RX2 MIX1 and RX3 MIX1

The kcontrol for the third input (rxN_mix1_inp3) of both RX2
and RX3 mixers are not using the correct control register. This simple
patch fixes this.

Signed-off-by: Jean-François Têtu <jean-francois.tetu@savoirfairelinux.com>
Signed-off-by: Mark Brown <broonie@kernel.org>