decoder: fix mini object implementation on 64-bit systems.
decoder: fix mini object implementation on 64-bit systems.

Use GPOINTER_TO_SIZE() instead of GPOINTER_TO_UINT() while manipulating
pointers. The latter is meant to be 32-bit only, not uintptr_t like size.
Only a gsize can hold all bits of a pointer.

Thanks to Ouping Zhang for spotting this error.

gbeauchesne/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,CapOM/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,CapOM/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,CapOM/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi