Fix getActiveMicrophones vts failure.

As there could be no mic on the device, the active microphones may not
always exist. With currently implementation in qcom hal, we need to
start the stream to have active microphones. In that case, just check
the return value of the call.

Bug: 109787938
Test: vts-tradefed run vts --module VtsHalAudioV4_0Target
Change-Id: Ia9f5160a278d6c788f8f5eb17b8b276fe1d66076