Fix typo in audio input provider

Bug: None
Test: Local compile
Change-Id: Id996eaa35211587410d4871c9ed55247683c6edc
Reviewed-on: https://chromium-review.googlesource.com/1159392Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579971}

chromeos/services/assistant/platform/audio_input_provider_impl.cc

@@ -152,7 +152,7 @@ void AudioInputImpl::SetMicState(bool mic_open) {
 
 void AudioInputImpl::OnHotwordEnabled(bool enable) {
   default_on_ = enable;
-  if (default_on_ || mic_open)
+  if (default_on_)
     source_->Start();
   else
     source_->Stop();