Fix trivial warnings hidden by -isystem

Fix the trivial warnings that are hidden by the use of -isystem to
include frameworks/av and caught by -Werror.

Test: m -j checkbuild
Bug: 31751828
Change-Id: I155f9f772ce0a84b364313814cb7cf528b9de4eb
diff --git a/media/libmediaplayerservice/include/MediaPlayerInterface.h b/media/libmediaplayerservice/include/MediaPlayerInterface.h
index a01f7f2..e8d59a7 100644
--- a/media/libmediaplayerservice/include/MediaPlayerInterface.h
+++ b/media/libmediaplayerservice/include/MediaPlayerInterface.h
@@ -286,7 +286,7 @@
     }
 
     // Modular DRM
-    virtual status_t prepareDrm(const uint8_t uuid[16], const Vector<uint8_t>& drmSessionId) {
+    virtual status_t prepareDrm(const uint8_t /* uuid */[16], const Vector<uint8_t>& /* drmSessionId */) {
         return INVALID_OPERATION;
     }
     virtual status_t releaseDrm() {