RDMA/rtrs: Fix the last iu->buf leak in err path

RDMA/rtrs: Fix the last iu->buf leak in err path

[ Upstream commit 3bf3a7c6985c625f64e73baefdaa36f1c2045a29 ]

The last iu->buf will leak if ib_dma_mapping_error() fails.

Fixes: c0894b3ea69d ("RDMA/rtrs: core: lib functions shared between client and server modules")
Link: https://lore.kernel.org/r/1682384563-2-3-git-send-email-lizhijian@fujitsu.com
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>