Pull out duplicated copies of silent mode check

Also fix the error handling for the property_get.

This is part of preparation for the threadLoop() merge.

Change-Id: I6405190ea18146d1271575e1dfe9f279e8f36b17
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index a2ab680..2a5d805 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -859,6 +859,9 @@
         virtual uint32_t        idleSleepTimeUs() = 0;
         virtual uint32_t        suspendSleepTimeUs() = 0;
 
+        // Code snippets that are temporarily lifted up out of threadLoop() until the merge
+                    void        checkSilentMode_l();
+
     private:
 
         friend class AudioFlinger;