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
diff --git a/libgralloc/ionalloc.cpp b/libgralloc/ionalloc.cpp
index fd3abbc..311fd8f 100644
--- a/libgralloc/ionalloc.cpp
+++ b/libgralloc/ionalloc.cpp
@@ -177,7 +177,7 @@
     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();