lavapipe: Resolved write to pointer after free

Write to "alloc" pointer variable after free "alloc"

Fixes: d74ea2c117 ("llvmpipe: Implement dmabuf handling")

Signed-off-by: liuqiang <liuqiang@kylinos.cn>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Lucas Fryzek <lfryzek@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32292>

src/gallium/drivers/llvmpipe/lp_texture.c

@@ -1506,6 +1506,7 @@ llvmpipe_import_memory_fd(struct pipe_screen *screen,
       if (!ret) {
          free(alloc);
          *ptr = NULL;
+         return false;
       } else {
          *ptr = (struct pipe_memory_allocation*)alloc;
       }