logd: rename FlushToResult to FilterResult

This was a typo; the enum corresponds to the result of the 'Filter'
function, not the 'FlushTo' function.

Test: build
Change-Id: Ib46f0646570b6dbaac17ae9fc95c990128cdbe72
diff --git a/logd/LogReaderThread.h b/logd/LogReaderThread.h
index e48a3ca..907bc83 100644
--- a/logd/LogReaderThread.h
+++ b/logd/LogReaderThread.h
@@ -63,8 +63,8 @@
   private:
     void ThreadFunction();
     // flushTo filter callbacks
-    FlushToResult FilterFirstPass(const LogBufferElement* element);
-    FlushToResult FilterSecondPass(const LogBufferElement* element);
+    FilterResult FilterFirstPass(const LogBufferElement* element);
+    FilterResult FilterSecondPass(const LogBufferElement* element);
 
     std::condition_variable thread_triggered_condition_;
     LogBuffer* log_buffer_;