Fix unnecessary DmaBuffer copying in getIonMappedSizeKb

Change the loop to access DmaBuffer by reference rather than copying it.

Bug: 138148041
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I47fb49deb46d24897d75f350f4b47679cad37542

core/jni/android_os_Debug.cpp

@@ -826,7 +826,7 @@ static jlong android_os_Debug_getIonMappedSizeKb(JNIEnv* env, jobject clazz) {
         }
     }
 
-    for (dmabufinfo::DmaBuffer buf : dmabufs) {
+    for (const dmabufinfo::DmaBuffer& buf : dmabufs) {
         ionPss += buf.size() / 1024;
     }