audio VTS: Fix call to IDevice::close in V6 tests

The result of RPC calls of HAL methods must be checked.
Added a check of result of calling IDevice::close added
for V6.

Bug: 114451103
Test: atest VtsHalAudioV6_0TargetTest
Change-Id: Ib6276382f15f122b43f314cf64cac2c3242bb76c