gralloc: use new API for Ion handles

The userspace API for Ion handles has changed slightly. Update to match
the new API.

Change-Id: I55e3ef4329f96eb6e368dbab493687b9fbc4ff49

libgralloc/ionalloc.cpp

@@ -177,7 +177,7 @@ int IonAlloc::clean_buffer(void *base, size_t size, int offset, int fd, int op)
     struct ion_flush_data flush_data;
     struct ion_fd_data fd_data;
     struct ion_handle_data handle_data;
-    struct ion_handle* handle;
+    ion_user_handle_t handle;
     int err = 0;
 
     err = open_device();