Fix A2dpAudioInterface getParameters.

A2dpAudioInterface::getParameters() was prepending a ';' to the key value pair returned from underlying AudioHardwareInterface.
diff --git a/libs/audioflinger/A2dpAudioInterface.cpp b/libs/audioflinger/A2dpAudioInterface.cpp
index 351815b..c07bbfe 100644
--- a/libs/audioflinger/A2dpAudioInterface.cpp
+++ b/libs/audioflinger/A2dpAudioInterface.cpp
@@ -185,7 +185,9 @@
     String8 keyValuePairs  = a2dpParam.toString();
 
     if (param.size()) {
-        keyValuePairs += ";";
+        if (keyValuePairs != "") {
+            keyValuePairs += ";";
+        }
         keyValuePairs += mHardwareInterface->getParameters(param.toString());
     }