zink: fix free of ralloced pointer
When we alloc with ralloc, we also need to free with it.
But let's take a step back here; we don't just need to use ralloc, we also need to destroy all other screen-resources. So let's call the destructor here instead.
Fixes: 2643f9ed ("zink: ralloc screen objects")
Edited by Erik Faye-Lund