Camera: fix bufferFreed callback object lifecycle issue

Make sure the callback object won't be freed in the middle
of callback execution.

Test: CTS + stress test
Bug: 63683767
Change-Id: I6fb1b754cadb3d499c1c246687d2f60d444d00bb
diff --git a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
index e15aa43..b02cd6a 100644
--- a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
@@ -727,7 +727,7 @@
 
 void Camera3OutputStream::onBuffersRemovedLocked(
         const std::vector<sp<GraphicBuffer>>& removedBuffers) {
-    Camera3StreamBufferFreedListener* callback = mBufferFreedListener;
+    sp<Camera3StreamBufferFreedListener> callback = mBufferFreedListener.promote();
     if (callback != nullptr) {
         for (auto gb : removedBuffers) {
             callback->onBufferFreed(mId, gb->handle);