MLK-20102 sound: asoc: fix VAD channel select

MLK-20102 sound: asoc: fix VAD channel select

The documentation specifies that VADCHSEL is used to select
the channel number on which hwvad detector will work. However,
we have used this field wrong (similar to the recording where
you can enable, disable multiple channels at the time).
This patch fixes hwvad and you can enable it by writing 0 to 7
in /sys/devices/platform/30080000.micfil/hwvad/enable or any
other number to disable it.

Signed-off-by: Cosmin-Gabriel Samoila <cosmin.samoila@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
(cherry picked from commit 4fdc1ca670db2f93362e8abde2707d98a7e450ff)