fix filter event creation

Change I154eb05bc419f827008161f85a6304a8599dc399 was incomplete and
caused some filter events to not be produced anymore. This change fixes
that issue and moves to a cleaner (and clearer!) way of creating filter events.
Note: Change I154eb05bc419f827008161f85a6304a8599dc399 did not break
VTS which is problematic.

Test: atest VtsHalTvTunerTargetTest
Bug: 183057734
Change-Id: Id018c33c16c07a9dd9de725aea64207008d317b3