Audio HAL VTS: setGain allow -0.0

Previously -0.0 was consider an invalid value as not in the range [0,1].
But it is quite difficult in C++ to differentiate -0.0 and 0.0 as -0.0 == 0.0
and such difference has no impact in practice.

Thus leave the implementation support or not -0.0.

Test: vts-tradefed run vts --module VtsHalAudioV2_0Target
Test: call/play music/record/video...
Bug: 36311550
Change-Id: Ia0ebcb325f77adcf8471620f418da1cbe8995e36
Signed-off-by: Kevin Rocard <krocard@google.com>