config: lito: add default value for ADC2_MIXER Switch

When restarting audioserver during SVA session, the default value
of ADC2_MIXER Swtich is not set to default value and cause SVA fail
to detect anything. Add default value for this mixer control.

Change-Id: Iebb1b818383e4735b98a63b35ccc4ef8a737a419
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>