rusticl/mesa: fix NULL pointer access in set_constant_buffer_stream

Fixes: b3133e250e ("gallium: add pipe_context::resource_release to eliminate buffer refcounting")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37311>

src/gallium/frontends/rusticl/mesa/pipe/context.rs

@@ -490,7 +490,8 @@ impl PipeContext {
                 idx,
                 &cb,
             );
-            self.pipe.as_ref().resource_release.unwrap()(self.pipe.as_ptr(), releasebuf);
+
+            pipe_resource_release(self.pipe.as_ptr(), releasebuf);
 
             true
         }