Use GraphicBuffer::toAHardwareBuffer() instead of casting

Test: build
Change-Id: I29a9b02a86d6163f7a181ed150a99987eaa61d45
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index 2bf8ff7..1efd98b 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -1493,7 +1493,7 @@
     int result = mGraphicBufferProducer->getLastQueuedBuffer(&graphicBuffer, &spFence, matrix);
 
     if (graphicBuffer != nullptr) {
-        *buffer = reinterpret_cast<AHardwareBuffer*>(graphicBuffer.get());
+        *buffer = graphicBuffer->toAHardwareBuffer();
         AHardwareBuffer_acquire(*buffer);
     } else {
         *buffer = nullptr;