RDMA/rtrs-srv: Free srv_mr iu only when always_invalidate is true

[ Upstream commit 3a71cd6c ]

Since srv_mr->iu is allocated and used only when always_invalidate is
true, free it only when always_invalidate is true.

Fixes: 9cb83748

 ("RDMA/rtrs: server: main functionality")
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Grzegorz Prajsner <grzegorz.prajsner@ionos.com>
Link: https://lore.kernel.org/r/20231120154146.920486-5-haris.iqbal@ionos.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>