afs: Fix potential null pointer dereference in afs_put_server

afs: Fix potential null pointer dereference in afs_put_server

afs_put_server() accessed server->debug_id before the NULL check, which
could lead to a null pointer dereference. Move the debug_id assignment,
ensuring we never dereference a NULL server pointer.

Fixes: 2757a4dc1849 ("afs: Fix access after dec in put functions")
Cc: stable@vger.kernel.org
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Acked-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>