Fix TunerFilterSetting union usage

This has been wrong and aosp/2001132 revealed it. Getting union value
should be done via get<Tag>() but the code was using "enum" constant for
getting isPassthrough value. (Previously, it was implicitly converted to
'true', but with aosp/2001132 implicit conversion is not available from
Tag to bool.)

"Merged-In"(I8400fd75080971ee897e1e2dc35e2bab45ec1659) is used to prevent
the change from being merged to internal branches.

Bug: 224692780
Test: mmma frameworks/av
Merged-In: I8400fd75080971ee897e1e2dc35e2bab45ec1659
Change-Id: Ic737b2a4a345ca3e1cf5019dad135348ab9c6f59