Radio, SoundTrigger: get service by value.

Get strong pointer to service interface by value and not reference to
prevent race conditions where the service pointer can be cleared
by another thread while in use.

Bug: 30907212
Change-Id: I6f02ec3fd1e6392b842b334e1cc4f9aa23916009
diff --git a/include/radio/Radio.h b/include/radio/Radio.h
index 302bf16..a4dfdd1 100644
--- a/include/radio/Radio.h
+++ b/include/radio/Radio.h
@@ -75,7 +75,7 @@
 private:
             Radio(radio_handle_t handle,
                             const sp<RadioCallback>&);
-            static const sp<IRadioService>& getRadioService();
+            static const sp<IRadioService> getRadioService();
 
             Mutex                   mLock;
             sp<IRadio>              mIRadio;