Fix getParameters() default implementation.

Do not return empty string but key value pairs with empty values.
diff --git a/libs/audioflinger/AudioHardwareInterface.cpp b/libs/audioflinger/AudioHardwareInterface.cpp
index 37be329..9a4a7f9 100644
--- a/libs/audioflinger/AudioHardwareInterface.cpp
+++ b/libs/audioflinger/AudioHardwareInterface.cpp
@@ -140,8 +140,8 @@
 // default implementation
 String8 AudioHardwareBase::getParameters(const String8& keys)
 {
-    String8 result = String8("");
-    return result;
+    AudioParameter param = AudioParameter(keys);
+    return param.toString();
 }
 
 // default implementation