stringify works with define, not enum.

Fixes: 91fddedd ("RDMA/rtrs: private headers with rtrs protocol structs and helpers")
Cc: jinpu.wang@ionos.com
Link: https://lore.kernel.org/r/20220712103113.617754-2-haris.iqbal@ionos.comSigned-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Reviewed-by: Aleksei Marov <aleksei.marov@ionos.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>