kopper: Do not free the given screen in initScreen implementation

The given screen is already freed by the caller in case a NULL-pointer is
returned by the implementation.

Cc: mesa-stable
Signed-off-by: Corentin Noël <corentin.noel@collabora.com>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20933>

src/gallium/frontends/dri/kopper.c

@@ -171,7 +171,6 @@ fail:
    dri_destroy_screen_helper(screen);
    if (screen->dev)
       pipe_loader_release(&screen->dev, 1);
-   FREE(screen);
    return NULL;
 }