Don't call operator== with scoped_ptr<T> and T*

That won't work when rtc::scoped_ptr becomes a type alias for
std::unique_ptr.

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1834103002

Cr-Commit-Position: refs/heads/master@{#12145}

webrtc/api/java/jni/androidmediadecoder_jni.cc

@@ -463,7 +463,7 @@ int32_t MediaCodecVideoDecoder::ReleaseOnCodecThread() {
 }
 
 void MediaCodecVideoDecoder::CheckOnCodecThread() {
-  RTC_CHECK(codec_thread_ == ThreadManager::Instance()->CurrentThread())
+  RTC_CHECK(codec_thread_.get() == ThreadManager::Instance()->CurrentThread())
       << "Running on wrong thread!";
 }