radv: free attachments on end command buffer.

radv: free attachments on end command buffer.

If we allocate attachments in the begin command buffer due to the
render pass continue bit, we were leaking them.

Since renderpasses inside a cmd buffer malloc/free these properly,
and set to NULL, we just need to call free at end.

Fixes a memory leak with multithreading demo.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: "17.2 17.3" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>