iris: close screen fd on iris_destroy_screen

Otherwise it never gets closed, this fixes errors seen with deqp-egl
where we end up opening 1024 files.

Fixes: 2dce0e94 ("iris: Initial commit of a new 'iris' driver for Intel Gen8+ GPUs.")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/gallium/drivers/iris/iris_screen.c

@@ -525,6 +525,7 @@ iris_destroy_screen(struct pipe_screen *pscreen)
    u_transfer_helper_destroy(pscreen->transfer_helper);
    iris_bufmgr_destroy(screen->bufmgr);
    disk_cache_destroy(screen->disk_cache);
+   close(screen->fd);
    ralloc_free(screen);
 }